Power conditioner and power conversion system

Abstract

In the present invention, a command value limiter applies limits to command values which are issued by a host device and which are for charging power and discharging power. A drive signal generator generates a drive signal for an inverter circuit in accordance with a command value for charging power limited by the command value limiter or a command value for discharging power limited by the command value limiter. A PI controller, in response to a direct-current voltage that is applied to the inverter circuit being higher than the working voltage of a charging limiter, calculates a PI control value (a PI control value for limiting charging) for the deviation between the direct-current voltage and the working voltage of the charging limiter and, in response to the direct-current voltage being lower than the working voltage of a discharging limiter, calculates a PI control value (a PI control value for limiting discharging) for the deviation between the direct-current voltage and the working voltage of the discharging limiter. A limiter regulator strengthens limitation of the command value for charging power from the command value limiter in accordance with the PI control value for limiting charging and strengthens limitation of the command value for discharging power from the command value limiter in accordance with the PI control value for limiting discharging.

Description

[Technical field]

[0001] The present disclosure relates to a power conditioner and a power conversion system including the same. [Background technology]

[0002] There is known a technology in which a storage battery is connected to an AC power system via a power conditioner to suppress power fluctuations in the AC power system using the storage battery. By controlling a gate pulse input to an inverter circuit of the power conditioner, it is possible to convert AC power in the AC power system to DC power and charge the storage battery, or to inversely convert the DC power of the storage battery back to AC power and discharge it to the AC power system. In a conventional power conditioner, a gate pulse signal that drives the inverter circuit is controlled according to a command from a higher-level device. As an example of the higher-level device, an energy management system (EMS) disclosed in JP 2015-149840 A is known. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-149840 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, power conditioners generally do not grasp the operating information of the storage battery, including the state of charge (SOC). Therefore, if the upper device mistakenly inputs a command to the power conditioner to overcharge the battery, the power conditioner will operate according to the charging power command value as is, which may result in overcharging of the storage battery. Similarly, if the power conditioner operates according to the power command value commanded by the upper device that may cause overdischarge, it may result in overdischarge of the storage battery.

[0005] An object of the present disclosure is to provide a power conditioner that can prevent at least one of overcharging and overdischarging of a storage battery with a simple configuration. [Means for solving the problem]

[0006] According to a first aspect of the present disclosure, a power conditioner includes an inverter circuit that connects an AC power system and a storage battery, a command value limiter, a drive signal generator, a PI controller, and a limiter adjuster. According to the first aspect of the present disclosure, the command value limiter, the drive signal generator, the PI controller, and the limiter adjuster are configured as follows.

[0007] The command value limiter is configured to limit a command value of the charging power commanded from the upper device and a command value of the discharging power commanded from the upper device. The drive signal generator is configured to generate a drive signal for the inverter circuit according to the command value of the charging power limited by the command value limiter or the command value of the discharging power limited by the command value limiter. The PI controller is configured to calculate a PI control value for charge limiting, which is a PI control value for a deviation between the DC voltage and the charging limiter operating voltage, in response to the DC voltage applied to the inverter circuit being higher than a predetermined charging limiter operating voltage. The PI controller is also configured to calculate a PI control value for discharge limiting, which is a PI control value for a deviation between the DC voltage and the discharging limiter operating voltage, in response to the DC voltage applied to the inverter circuit being lower than a predetermined discharging limiter operating voltage. The limiter adjuster is configured to strengthen the limit on the command value of the charging power by the command value limiter in accordance with the PI control value for charge limiting. The limiter adjuster is also configured to strengthen the limitation on the command value of the discharge power by the command value limiter in accordance with the PI control value for limiting discharge.

[0008] The command value limiter may be configured to multiply the command value of the charging power by a charge limit gain having a value of 0 or more and 1 or less, and to multiply the command value of the discharging power by a discharge limit gain having a value of 0 or more and 1 or less. The limiter regulator may be configured to reduce the charge limit gain in accordance with the PI control value for the charging limit, and to reduce the discharge limit gain in accordance with the PI control value for the discharging limit. Furthermore, the limiter regulator may be configured to maintain the charge limit gain at zero while the PI control value for the charging limit is outside a predetermined range. The limiter regulator may be configured to maintain the discharge limit gain at zero while the PI control value for the discharging limit is outside a predetermined range.

[0009] According to a second aspect of the present disclosure, a power conditioner includes an inverter circuit that connects an AC power system and a storage battery, a command value limiter, a drive signal generator, a PI controller, and a limiter adjuster. According to the second aspect of the present disclosure, the command value limiter, the drive signal generator, the PI controller, and the limiter adjuster are configured as follows.

[0010] The command value limiter is configured to impose a limit on a command value of the charging power commanded from a higher-level device. The drive signal generator is configured to generate a drive signal for the inverter circuit according to the command value of the charging power limited by the command value limiter. The PI controller is configured to calculate a PI control value for charging limiting, which is a PI control value for a deviation between the DC voltage and the charging limiter operating voltage, in response to the DC voltage applied to the inverter circuit being higher than a predetermined charging limiter operating voltage. The limiter adjuster is configured to strengthen the limit on the command value of the charging power by the command value limiter in accordance with the PI control value for charging limiting.

[0011] The command value limiter may be configured to multiply the command value of the charging power by a charging limit gain having a value equal to or greater than 0 and equal to or less than 1. The limiter adjuster may be configured to reduce the charging limit gain in response to a PI control value for charging limit. Furthermore, the limiter adjuster may be configured to maintain the charging limit gain at zero while the PI control value for charging limit is outside a predetermined range.

[0012] According to a third aspect of the present disclosure, a power conditioner includes an inverter circuit that connects an AC power system and a storage battery, a command value limiter, a drive signal generator, a PI controller, and a limiter adjuster. According to the third aspect of the present disclosure, the command value limiter, the drive signal generator, the PI controller, and the limiter adjuster are configured as follows.

[0013] The command value limiter is configured to impose a limit on a command value of the discharge power commanded from a higher-level device. The drive signal generator is configured to generate a drive signal for the inverter circuit according to the command value of the discharge power limited by the command value limiter. The PI controller is configured to calculate a PI control value for discharge limiting, which is a PI control value for the deviation between the DC voltage and the discharge limiter operation voltage, in response to the DC voltage applied to the inverter circuit being lower than a predetermined discharge limiter operation voltage. The limiter adjuster is configured to strengthen the limit on the command value of the discharge power by the command value limiter in accordance with the PI control value for discharge limiting.

[0014] The command value limiter may be configured to multiply the command value of the discharge power by a discharge limit gain having a value equal to or greater than 0 and equal to or less than 1. The limiter adjuster may be configured to reduce the discharge limit gain in accordance with a PI control value for discharge limit. Furthermore, the limiter adjuster may be configured to maintain the discharge limit gain at zero while the PI control value for discharge limit is outside a predetermined range.

[0015] The present disclosure also provides a power conversion system. According to one aspect of the present disclosure, the power conversion system includes one or more power conditioners connected to a common AC power system, and a host device that issues a command value of charge power or a command value of discharge power to the one or more power conditioners. The one or more power conditioners are the power conditioners according to any one of the first to third aspects of the present disclosure. Effect of the Invention

[0016] According to the present disclosure, at least one of overcharging and overdischarging of a storage battery can be prevented with a simple configuration. In particular, by strengthening the limit on the command value of the charging power by the command value limiter according to the PI control value for the deviation between the DC voltage and the charging limiter operating voltage, chattering of the command value limiter caused by voltage fluctuations can be suppressed and charging operation can be continued as long as possible. Also, by strengthening the limit on the command value of the discharging power by the command value limiter according to the PI control value for the deviation between the DC voltage and the discharging limiter operating voltage, chattering of the command value limiter caused by voltage fluctuations can be suppressed and discharging operation can be continued as long as possible. [Brief description of the drawings]

[0017] [Figure 1] 1 is a diagram showing a configuration of a power conditioner according to an embodiment of the present disclosure, and a configuration of a power conversion system using the power conditioner; [Diagram 2] FIG. 11 is a diagram showing the relationship between the charge limiter operating voltage value and the discharge limiter operating voltage value and the voltage range of the power conditioner and the voltage range of the storage battery. [Diagram 3] FIG. 2 is a diagram illustrating an example of a configuration of a PI controller according to an embodiment of the present disclosure. [Figure 4] 1A to 1C are diagrams illustrating an overcharge prevention operation of a power conditioner according to an embodiment of the present disclosure. [Diagram 5] 1A to 1C are diagrams illustrating an over-discharge prevention operation of a power conditioner according to an embodiment of the present disclosure. [Figure 6]1A and 1B are diagrams illustrating an example of voltage and current behavior during a typical charging operation of a storage battery, and an example of voltage and current behavior during charging and discharging using a conventional power conditioner. [Figure 7] 1A to 1C are diagrams illustrating an example of voltage and current behavior during charging by a power conditioner according to an embodiment of the present disclosure, and an example of voltage and current behavior during discharging. [Figure 8] 1 is a diagram illustrating a first specific example of a configuration of a control device for a power conditioner according to an embodiment of the present disclosure. [Figure 9] 11 is a diagram illustrating a second specific example of the configuration of a control device of a power conditioner according to an embodiment of the present disclosure. FIG. [Figure 10] FIG. 13 is a diagram illustrating a third specific example of the configuration of a control device of a power conditioner according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] 1. Power conditioner configuration Hereinafter, a power conditioner according to an embodiment of the present disclosure will be described with reference to the drawings. The power conditioner is also called a power conditioning system and is generally abbreviated as PCS. In this specification, the power conditioner is also abbreviated as PCS.

[0019] FIG. 1 is a diagram showing a configuration of a PCS10 according to an embodiment of the present disclosure, and a configuration of a power conversion system 2 using the PCS10. The power conversion system 2 is a distributed power supply system for grid connection that combines a higher-level device 4 with a single or multiple PCSs 10. For convenience, only one PCS 10 is illustrated in the example shown in FIG. 1. A storage battery 6 is connected to each PCS 10. The higher-level device 4 is a controller that issues charging or discharging commands to each PCS 10 constituting the power conversion system 2. An example of the higher-level device 4 is an EMS.

[0020] The PCS 10 includes a system connection terminal 14 to which a three-phase AC power system (not shown) is connected, and a DC power supply connection terminal 12 to which the storage battery 6 is connected. Inside the PCS 10, a three-phase inverter circuit 20 is provided that converts AC power from the AC power system to DC power and inversely converts the DC power from the storage battery 6 to three-phase AC power. Note that the AC power system may be single-phase. In that case, a single-phase inverter circuit is provided inside the PCS 10.

[0021] A smoothing circuit 30 for smoothing the DC current is provided between the DC power supply connection terminal 12 and the inverter circuit 20. The smoothing circuit is composed of a resistor and a capacitor. A DC current breaker 40 for interrupting the DC current is provided between the DC power supply connection terminal 12 and the smoothing circuit 30. In addition, an AC current breaker 50 for interrupting the three-phase AC current is provided between the system connection terminal 14 and the inverter circuit 20.

[0022] A voltmeter 80 is provided within the PCS 10. The voltmeter 80 measures the DC input voltage generated between the positive and negative electrodes of the DC power supply connection terminals 12. Alternatively, the voltmeter 80 may be installed between the smoothing circuit 30 and the DC current breaker 40 to measure the DC capacitor voltage of the smoothing circuit 30. The DC voltage measured by the voltmeter 80 is input to the control device 100, which will be described next.

[0023] A control device 100 is provided within the PCS 10. The control device 100 controls the charging and discharging operations of the PCS 10. Commands from the higher-level device 4 are input to the control device 100. The commands input from the higher-level device 4 to the control device 100 include an active power command value for discharging power for discharging power from the storage battery 6 to the AC power system (hereinafter referred to as a discharging power command value), and an active power command value for charging power for charging power from the AC power system to the storage battery 6 (hereinafter referred to as a charging power command value). The discharging power command value is a power command value that takes a value within the range of 0 to 100%. The charging power command value is a power command value that takes a value within the range of -100 to 0%.

[0024] The controller 100 may be an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a central processing unit (CPU), or another device. Alternatively, the controller 100 may be a combination of two or more ASICs, FPGAs, CPUs, or another device. The ASICs, FPGAs, CPUs, and other devices corresponding to the controller 100 include a set of executable instructions. When the instructions are executed, the corresponding ASICs, FPGAs, CPUs, and other devices are triggered to perform functions described below. The instructions may be stored on a storage medium or may be embedded in the corresponding ASICs or FPGAs.

[0025] 1 shows functions of the control device 100 in blocks. The control device 100 includes a drive signal generator 110, a command value limiter 120, a voltage limit range setter 130, a voltage deviation calculator 140, a PI controller 150, and a limiter adjuster 160. These functions are executed in a corresponding ASIC, FPGA, CPU, or another device by executing a series of instructions.

[0026] The drive signal generator 110 has a gate pulse generating circuit that drives the switching elements of the inverter circuit 20. The drive signal generator 110 receives an input of a power command value and generates a gate pulse signal so that the output power of the inverter circuit 20 becomes the power command value. When the input power command value is a charge power command value, the drive signal generator 110 generates a gate pulse signal that drives the inverter circuit 20 so that the storage battery 6 is charged from the AC power system. When the input power command value is a discharge power command value, the drive signal generator 110 generates a gate pulse signal that drives the inverter circuit 20 so that the storage battery 6 is discharged to the AC power system.

[0027] The command value limiter 120 imposes a limit on the power command value input from the higher-level device 4 to the drive signal generator 110. The power command value input to the drive signal generator 110 is the power command value to which the limit has been imposed by the command value limiter 120. When the power command value is a charge power command value that takes a negative value, imposing a limit on the power command value means correcting the power command value to a command value with a higher value (a command value closer to zero). As a specific example, the command value limiter 120 multiplies the charge power command value by a charge limit gain having a value between 0 and 1. The limit on the charge power command value imposed by the command value limiter 120 is automatically adjusted by a limiter adjuster 160 described later.

[0028] When the command from the higher-level device 4 to the PCS 10 is a discharge command, the power command value input to the drive signal generator 110 takes a positive value. When the power command value is a discharge power command value taking a positive value, applying a limit to the power command value means correcting the power command value to a lower command value (a command value closer to zero). As a specific example, the command value limiter 120 multiplies the discharge power command value by a discharge limit gain having a value between 0 and 1. The limit on the discharge power command value by the command value limiter 120 is also automatically adjusted by the limiter adjuster 160 described later.

[0029] The voltage limit range setting device 130 stores a preset charge limiter operating voltage and a preset discharge limiter operating voltage. The charge limiter operating voltage is a voltage that triggers the overcharge prevention operation of the PCS 10. The discharge limiter operating voltage is a voltage that triggers the overdischarge prevention operation of the PCS 10. The concept of setting the charge limiter operating voltage and the discharge limiter operating voltage will be described later.

[0030] The voltage deviation calculator 140 reads the charge limiter operating voltage and the discharge limiter operating voltage from the voltage limit range setter 130. The voltage deviation calculator 140 also acquires the DC voltage measured by the voltmeter 80 at regular intervals. Every time the measured DC voltage is acquired from the voltmeter 80, the voltage deviation calculator 140 compares the measured DC voltage with the charge limiter operating voltage and also compares the measured DC voltage with the discharge limiter operating voltage. However, the measured DC voltage used in the comparison is not an instantaneous value but a moving average value over a predetermined period.

[0031] When the measured DC voltage is higher than the charge limiter operating voltage, the voltage deviation calculator 140 outputs the deviation of the measured DC voltage from the charge limiter operating voltage. When the measured DC voltage is lower than the discharge limiter operating voltage, the voltage deviation calculator 140 outputs the deviation of the measured DC voltage from the discharge limiter operating voltage. When the measured DC voltage is equal to or lower than the charge limiter operating voltage and equal to or higher than the discharge limiter operating voltage, the voltage deviation calculator 140 sets the output value to zero.

[0032] The output of the voltage deviation calculator 140 is input to the PI controller 150. The PI controller 150 calculates a PI control value for the output of the voltage deviation calculator 140. More specifically, the PI controller 150 calculates a PI control value for the deviation between the charge limiter operating voltage and the measured DC voltage, and a PI control value for the deviation between the discharge limiter operating voltage and the measured DC voltage. The former is a PI control value calculated when the measured DC voltage is higher than the charge limiter operating voltage, and is used for limiting charging. The latter is a PI control value calculated when the measured DC voltage is lower than the discharge limiter operating voltage, and is used for limiting discharging. A formula for calculating the PI control value for charging limiting and a formula for calculating the PI control value for discharging limiting are defined separately.

[0033] The PI control value for charge limit and the PI control value for discharge limit calculated by the PI controller 150 are input to the limiter regulator 160. The limiter regulator 160 strengthens the limit on the command value of the charging power by the command value limiter 120 according to the PI control value for charge limit. When a deviation occurs between the measured DC voltage and the charge limiter operating voltage, the PI control value for charge limit changes in one direction, either the positive or negative side. Whether it changes to the positive or negative side depends on the proportional gain setting of the PI control.

[0034] Until the PI control value for charging limit changes from the initial value to a predetermined threshold, the limiter adjuster 160 linearly strengthens the restriction by the command value limiter 120 with respect to the change in the PI control value for charging limit. As a specific example, the limiter adjuster 160 brings the charging limit gain closer to zero from 1 as the PI control value for charging limit approaches the threshold. Then, the limiter adjuster 160 sets the charging limit gain to zero when the PI control value for charging limit reaches the threshold, and maintains the charging limit gain at zero while the PI control value for charging limit is outside a predetermined range defined by the threshold.

[0035] Furthermore, the limiter adjuster 160 strengthens the limit on the command value of the discharge power by the command value limiter 120 according to the PI control value for limiting discharge. When a deviation occurs between the measured DC voltage and the discharge limiter operating voltage, the PI control value for limiting discharge changes in one direction, either the positive or negative side. Whether the change is to the positive or negative side depends on the proportional gain setting of the PI control.

[0036] Until the PI control value for discharge limiting changes from the initial value to a predetermined threshold, the limiter adjuster 160 linearly strengthens the limitation by the command value limiter 120 in response to the change in the PI control value for discharge limiting. As a specific example, the limiter adjuster 160 brings the discharge limit gain closer to zero from 1 as the PI control value for discharge limiting approaches the threshold. Then, the limiter adjuster 160 sets the discharge limit gain to zero when the PI control value for discharge limiting reaches the threshold, and maintains the discharge limit gain at zero while the PI control value for discharge limiting is outside a predetermined range defined by the threshold.

[0037] 2. Operation of the power conditioner Next, the operation of the PCS 10 configured as above, and in particular the operation of the control device 100, will be described.

[0038] First, before describing the operation of the control device 100, a description will be given of the charge limiter operating voltage and the discharge limiter operating voltage set by the voltage limit range setter 130. The charge limiter operating voltage and the discharge limiter operating voltage are set in consideration of the operating voltage range of the PCS 10 and the voltage range of the storage battery 6. Fig. 2 is a diagram showing the relationship between the charge limiter operating voltage value VdclimL and the discharge limiter operating voltage value VdclimH and the operating voltage range of the PCS 10 and the voltage range of the storage battery 6.

[0039] As shown in Example 1 of FIG. 2, the operating voltage range of the PCS 10 is generally set to the voltage range of the storage battery 6. In this case, the lower limit operating voltage of the PCS 10 coincides with the lower limit voltage of the storage battery 6 and is set as the system lower limit voltage Vdcmin. The discharge limiter operating voltage value VdclimL is set to a voltage higher than the system lower limit voltage Vdcmin. For example, when the system lower limit voltage Vdcmin is 710V, the discharge limiter operating voltage value VdclimL is set to 720V. Also, the upper limit operating voltage of the PCS 10 coincides with the upper limit voltage of the storage battery 6 and is set as the system upper limit voltage Vdcmax. The charge limiter operating voltage value VdclimH is set to a voltage lower than the system upper limit voltage Vdcmax. For example, when the system upper limit voltage Vdcmax is 1100V, the charge limiter operating voltage value VdclimH is set to 1090V.

[0040] Also, as shown in Example 2 of FIG. 2, there may be a discrepancy between the operating voltage range of the PCS 10 and the voltage range of the storage battery 6. In this case, the higher of the lower limit operating voltage of the PCS 10 and the lower limit voltage of the storage battery 6 is set as the system lower limit voltage Vdcmin. Also, the lower of the upper limit operating voltage of the PCS 10 and the upper limit voltage of the storage battery 6 is set as the system upper limit voltage Vdcmax. For example, when the operating voltage range of the PCS 10 is 710 to 1100V and the voltage range of the storage battery 6 is 950 to 1300V, the system lower limit voltage Vdcmin is set to 950V and the system upper limit voltage Vdcmax is set to 1100V. The charge limiter operating voltage value VdclimL is set to a voltage higher than the system lower limit voltage Vdcmin. The discharge limiter operating voltage value VdclimH is set to a voltage lower than the system upper limit voltage Vdcmax. However, since the upper limit operating voltage of the PCS 10 is lower than the upper limit voltage of the storage battery 6, the storage battery 6 will not be overcharged even if it is close to the upper limit operating voltage of the PCS 10. Therefore, in the case of Example 2, it is not necessary to limit the output within the range from the discharge limiter activation voltage value VdclimH to the system upper limit voltage Vdcmax.

[0041] One element that determines the operation of the PCS 10 is the PI controller 150. The PI controller 150 is configured to operate differently during charging and discharging. FIG. 3 is a diagram showing an example of the configuration of the PI controller 150. The configuration of the PI controller 150 shown in the upper part of FIG. 3 is the configuration of the PI controller 150 for charge control used during charging. The configuration of the PI controller 150 shown in the lower part of FIG. 3 is the configuration of the PI controller 150 for discharge control used during discharging. The PI controller 150 is composed of a feedback control unit 150a and a limiter conversion unit 150b. However, feedback control units 150a with different configurations are used for charge control and discharge control. Also, limiter conversion units 150b with different configurations are used for charge control and discharge control.

[0042] First, the configuration for charge control will be described. The feedback control unit 150a for charge control includes a proportional integrator having a transfer function G02 expressed by the following formula (1). In the following formula (1), Kp2 is a proportional gain for charge control, and T2 is a time constant for charge control.

number

[0043] Using the transfer function G02, the equation for calculating the output Y(s) of the feedback control unit 150a for charging control is expressed by the following formula (2). The feedback control unit 150a makes the output Y(s) follow the input X(s) with the input X(s) as a target value. Note that the input X(s) in the following formula (2) is the deviation Vdcerr between the measured DC voltage Vdcfbk and the charging limiter activation voltage value VdclimH.

number

[0044] The limiter conversion unit 150b for charge control converts the output of the feedback control unit 150a into a PI control value G2 for limiting charge. For this conversion, a charge limiter gain K2 expressed by the following formula (3) is used. The output of the feedback control unit 150a is converted from a voltage to a dimensionless quantity by proportional control using the charge limiter gain K2.

number

[0045] When the above charge limiter gain K2 is used, an equation for calculating a PI control value G2 for limiting charge is expressed by the following equation (4).

number

[0046] Next, the configuration for discharge control will be described. The feedback control unit 150a for discharge control includes a proportional integrator having a transfer function G01 expressed by the following formula (5). In the following formula (5), Kp1 is a proportional gain for discharge control, and T1 is a time constant for discharge control. The proportional gain Kp1 may be the same value as the proportional gain Kp2 for charge control, or may be set to a different value. The time constant T1 may be the same value as the time constant T2 for charge control, or may be set to a different value.

number

[0047] Using the transfer function G01, the equation for calculating the output Y(s) of the feedback control unit 150a for discharge control is expressed by the following formula (6). The feedback control unit 150a makes the output Y(s) follow the input X(s) with the input X(s) as a target value. Note that the input X(s) in the following formula (6) is the deviation Vdcerr between the measured DC voltage Vdcfbk and the discharge limiter activation voltage value VdclimL.

number

[0048] The limiter conversion unit 150b for discharge control converts the output of the feedback control unit 150a into a PI control value G1 for limiting discharge. For this conversion, a discharge limiter gain K1 expressed by the following equation (7) is used. The output of the feedback control unit 150a is converted from a voltage to a dimensionless quantity by proportional control using the discharge limiter gain K1.

number

[0049] When the above-mentioned discharge limiter gain K1 is used, the equation for calculating the PI control value G1 for limiting discharge is expressed by the following formula (8).

number

[0050] The operation of the PCS 10 includes an overcharge prevention operation for protecting the storage battery 6 from overcharging. A specific example of the overcharge prevention operation of the PCS 10 is shown in Fig. 4. When a charge command is input from the higher-level device 4 to the control device 100, a voltage deviation calculator 140 calculates a deviation Vdcerr between the measured DC voltage Vdcfbk and the charge limiter operating voltage value VdclimH. A PI controller 150 performs feedback control based on the deviation Vdcerr calculated by the voltage deviation calculator 140. When the sum of the P term and I term by the feedback control converges to the deviation Vdcerr, which is a target value, a PI control value G2 for limiting charging converges to a value expressed by the following equation (9).

number

[0051] The limiter adjuster 160 reduces the charge limit gain from 1 to zero in response to a change in the PI control value G2 for charge limit. Then, the command value limiter 120 limits the charge power command value Pref input from the higher-level device 4 by the charge limit gain adjusted by the limiter adjuster 160, and inputs the limited charge power command value Pref2 to the drive signal generator 110. When the charge limit gain is 1, the charge power command value Pref becomes the charge power command value Pref2 as it is, and when the charge limit gain is zero, the charge power command value Pref2 is set to zero.

[0052] The operation of the PCS 10 includes an over-discharge prevention operation for protecting the storage battery 6 from over-discharge. A specific example of the over-discharge prevention operation of the PCS 10 is shown in Fig. 5. When a discharge command is input from the higher-level device 4 to the control device 100, the voltage deviation calculator 140 calculates the deviation Vdcerr between the measured DC voltage Vdcfbk and the discharge limiter activation voltage value VdclimL. The PI controller 150 performs feedback control based on the deviation Vdcerr calculated by the voltage deviation calculator 140. When the sum of the P term and I term by the feedback control converges to the deviation Vdcerr, which is a target value, the PI control value G1 for limiting discharge converges to a value expressed by the following equation (10).

number

[0053] The limiter adjuster 160 reduces the discharge limit gain from 1 to zero in response to a change in the PI control value G1 for limiting discharge. Then, the command value limiter 120 limits the discharge power command value Pref input from the higher-level device 4 by the discharge limit gain adjusted by the limiter adjuster 160, and inputs the limited discharge power command value Pref2 to the drive signal generator 110. When the discharge limit gain is 1, the discharge power command value Pref becomes the discharge power command value Pref2 as it is, and when the discharge limit gain is zero, the discharge power command value Pref2 is set to zero.

[0054] As described above, in the overcharge prevention operation and overdischarge prevention operation by the control device 100, the charge limit gain and the discharge limit gain are calculated by the PI control value calculated using the proportional integral control, not the simple proportional control. If only the proportional control is used instead of the proportional integral control, the DC voltage may fluctuate due to the influence of the DC ripple caused by the voltage fluctuation of the storage battery 6 and the switching of the inverter circuit 20, and the charge limit gain or the discharge limit gain of the command value limiter 120 may fluctuate sharply. For example, if the battery is suddenly discharged 100% at the discharge end voltage, the DC voltage decreases. When the command value limiter 120 is activated in response to the decrease in the DC voltage, the DC voltage increases again. In the case of the simple proportional control, chattering may occur in this manner. However, when the charge limit gain and the discharge limit gain are calculated using the PI control value obtained by the proportional integral control, chattering does not occur because there is a time constant in the control response, and smooth control is possible.

[0055] In addition, by using a PI control system defined separately for the overcharge prevention operation and the overdischarge prevention operation, the operation of the command value limiter 120 can be realized according to the charge characteristic and the discharge characteristic of the storage battery 6. For example, since the voltage drop is steep in the overdischarge region as a characteristic of the storage battery 6, the PI control system for discharging limitation may be designed so that the overdischarge prevention operation of the command value limiter 120 is also accelerated. Specifically, the time constant T1 of the I term in the calculation formula of the PI control value G1 for discharging limitation can be shortened so that the overdischarge prevention operation of the command value limiter 120 is also accelerated. In addition, since the voltage fluctuation is gentle in the overcharge region, the PI control system for charging limitation may be designed so that the overcharge prevention operation of the command value limiter 120 is also gentle. Specifically, the time constant T2 of the I term in the calculation formula of the PI control value G2 for charging limitation can be lengthened so that the overcharge prevention operation of the command value limiter 120 is also gentle.

[0056] Here, the characteristics of the operation of the PCS 10 according to this embodiment will be described in comparison with the conventional technology. FIG. 6 shows an example of the voltage and current behavior in a general charging operation method of a storage battery. The thick line indicates the voltage, and the thin line indicates the current. The general charging operation method is a combination of constant voltage operation (CV operation) and constant current operation (CC operation) with direct current. More specifically, CC operation is performed from the beginning to the middle of the discharge operation and charging operation. Then, CC operation is switched to CV operation near the full charge voltage, and the battery is fully charged without overcharging. Since CV operation continues even after full charging, in principle, a current for compensating for the self-discharge of the battery continues to flow. However, the general charging operation method does not have a special function to prevent overdischarge of the storage battery. In the general charging operation method, the device is simply protected and stopped when the voltage drops to the protection stop voltage level of the device.

[0057] FIG. 6 also shows an example of the voltage and current behavior during charging and discharging with a conventional PCS. The thick line indicates the voltage, and the thin line indicates the current. The conventional PCS charges or discharges the storage battery directly according to the power command value from the upper device. Therefore, in the unlikely event that the current command value is abnormal, the storage battery may enter an overcharged or overdischarged state. In the conventional PCS, when the voltage rises to the overcharge voltage level, the PCS is stopped to protect the battery from overcharging, and when the voltage reaches the discharge voltage level, the PCS is stopped to protect the battery from overdischarging.

[0058] In contrast to the above-described conventional technology, the behavior of voltage and current during charging by the PCS 10 according to this embodiment is illustrated in FIG. 7. According to the PCS 10, when the voltage rises due to charging, the overcharge prevention operation functions, and the voltage can be gradually brought to the full charge voltage while monotonically lowering the current. This makes it possible to prevent the voltage from overshooting the overcharge voltage level. In addition, after the voltage reaches the full charge voltage, the voltage can be maintained at the full charge voltage. Furthermore, during that time, if the command value limiter 120 is not narrowed down completely to 0%, but is narrowed down to a few percent, the self-discharge compensation current can be continued to flow to the storage battery 6.

[0059] 7 also shows an example of the voltage and current behavior during discharge by the PCS 10 according to this embodiment. When the voltage drops due to discharge, the PCS 10's overdischarge prevention operation functions to gradually lower the current and allow the voltage to gradually reach the discharge termination voltage. This prevents a steep voltage drop in the overdischarge region and protects the storage battery 6 from overdischarge.

[0060] 3. Specific examples of the configuration of a power conditioner control device Next, a specific example of the configuration of the control device 100 will be described with reference to the drawings. Functions common to the specific examples will be denoted by common reference numerals, and description of those functions will be omitted or simplified.

[0061] <First concrete example> 8 is a diagram showing a first specific example of the configuration of the control device 100. In the first specific example, the command value limiter 120 is composed of a variable limiter 122. The variable limiter 122 limits the positive power command value Pref, i.e., the discharge power command value, to an upper limit value PreflimH. The upper limit value PreflimH is expressed as a percentage when the power command value Pref is set to 100%. When the power command value Pref is a positive value, the variable limiter 122 outputs the upper limit value PreflimH as the limited power command value Pref2.

[0062] Moreover, the variable limiter 122 limits a negative power command value Pref, i.e., a charging power command value, to a lower limit value PreflimL. The lower limit value PreflimL is expressed as a percentage when the power command value Pref is set to -100%. When the power command value Pref is a negative value, the variable limiter 122 outputs the lower limit value PreflimL as a limited power command value Pref2.

[0063] In the first specific example, the voltage deviation calculator 140 includes a limiter 142 and a subtractor 144. When the measured DC voltage Vdcfbk is a positive value, the limiter 142 compares the measured DC voltage Vdcfbk with the charge limiter operation voltage value VdclimH set by the voltage limit range setter 130. When the measured DC voltage Vdcfbk is less than the charge limiter operation voltage value VdclimH, the limiter 142 outputs the measured DC voltage Vdcfbk as it is as the limited measured DC voltage Vdclim. When the measured DC voltage Vdcfbk is equal to or greater than the charge limiter operation voltage value VdclimH, the limiter 142 outputs the charge limiter operation voltage value VdclimH as the limited measured DC voltage Vdclim.

[0064] When the measured DC voltage Vdcfbk is a negative value, the limiter 142 compares the measured DC voltage Vdcfbk with the discharge limiter operation voltage value VdclimL set by the voltage limit range setter 130. If the measured DC voltage Vdcfbk is greater than the discharge limiter operation voltage value VdclimL, the limiter 142 outputs the measured DC voltage Vdcfbk as is as the limited measured DC voltage Vdclim. If the measured DC voltage Vdcfbk is equal to or less than the discharge limiter operation voltage value VdclimL, the limiter 142 outputs the discharge limiter operation voltage value VdclimL as the limited measured DC voltage Vdclim.

[0065] The subtractor 144 calculates a deviation Vdcerr of the limited measured DC voltage Vdclim with respect to the measured DC voltage Vdcfbk. If the measured DC voltage Vdcfbk is equal to or greater than the charge limiter operating voltage value VdclimH, the deviation Vdcerr is the deviation between the charge limiter operating voltage value VdclimH and the measured DC voltage Vdcfbk. In this case, the deviation Vdcerr is a positive value. If the measured DC voltage Vdcfbk is equal to or less than the discharge limiter operating voltage value VdclimL, the deviation Vdcerr is the deviation between the discharge limiter operating voltage value VdclimL and the measured DC voltage Vdcfbk. In this case, the deviation Vdcerr is a negative value. If the measured DC voltage Vdcfbk is greater than the discharge limiter operating voltage value VdclimL and less than the charge limiter operating voltage value VdclimH, the deviation Vdcerr is zero.

[0066] As a specific example, the charge limiter operating voltage value VdclimH is set to 1090 V, and the discharge limiter operating voltage value VdclimL is set to 720 V. Furthermore, an example of the measured DC voltage Vdcfbk during charging is set to 1150 V, and an example of the measured DC voltage Vdcfbk during discharging is set to 716 V. In this case, the limited measured DC voltage Vdclim output from the limiter 142 during charging is 1090 V, and the deviation Vdcerr output from the subtractor 144 is −60 V. Furthermore, the limited measured DC voltage Vdclim output from the limiter 142 during discharging is set to 720 V, and the deviation Vdcerr output from the subtractor 144 is set to 4 V.

[0067] The PI controller 150 of the first specific example is a PI controller 152. The PI controller 152 calculates a PI control value G for the deviation Vdcerr calculated by the subtractor 144. The PI controller 152 switches between a configuration for charge control and a configuration for discharge control shown in Fig. 3. Therefore, the PI control value G output from the PI controller 152 during charging is a PI control value G2 for charge limiting. The PI control value G output from the PI controller 152 during discharging is a PI control value G1 for discharge limiting.

[0068] In the first specific example, however, the equation for calculating the PI control value G2 for charging limit is expressed by the following formula (11). The dimension of the PI control value G2 in the first specific example is a percentage. According to formula (11), if the deviation Vdcerr is -60V as in the example during charging described above, the PI control value G2 for charging limit is -600%.

number

[0069] In the first specific example, the equation for calculating the PI control value G1 for limiting discharge is expressed by the following formula (12). The dimension of the PI control value G1 in the first specific example is a percentage. According to formula (12), if the deviation Vdcerr is 4V as in the above example during discharge, the PI control value G1 for limiting discharge is 40%.

number

[0070] In the first specific example, the limiter adjuster 160 is composed of a discharge limit gain adjustment circuit made up of a limiter 162 and a subtractor 164, and a charge limit gain adjustment circuit made up of a limiter 166 and a subtractor 168. The discharge limit gain adjustment circuit is a circuit that adjusts the upper limit value PreflimH of the variable limiter 122 within a range from 100% to 0%. The charge limit gain calculation circuit is a circuit that adjusts the lower limit value PreflimL of the variable limiter 122 within a range from -100% to 0%. The discharge limit gain calculation circuit and the charge limit gain calculation circuit are connected in parallel to the PI controller 152.

[0071] The limiter 162 constituting the discharge limit gain calculation circuit limits the PI control value G (the PI control value G1 for limiting discharge) calculated by the PI controller 152 during discharge to within a range from 100% to 0%, and outputs the limited PI control value GH. In other words, if the PI control value G is 100% or less, the limiter 162 outputs the PI control value G as it is as the limited PI control value GH. If the PI control value G is higher than 100%, the limiter 162 outputs 100% as the limited PI control value GH. The subtractor 164 constituting the discharge limit gain calculation circuit subtracts the limited PI control value GH from 100%, which is a fixed value, and outputs the difference as the discharge limit gain. The discharge limit gain is set as the upper limit value PreflimH of the variable limiter 122.

[0072] When the PI control value G is 40% as in the above-mentioned example of discharging, the limited PI control value GH remains at 40%, and the upper limit value PreflimH is set to 60%. As a result, the power command value Pref that commands discharging is limited to 60% by the variable limiter 122, and the power command value Pref2 limited to 50% is input to the drive signal generator 110.

[0073] The limiter 166 constituting the charging limit gain calculation circuit limits the PI control value G (the PI control value G2 for charging limit) calculated by the PI controller 152 during charging to within a range from -100% to 0%, and outputs the limited PI control value GL. That is, if the PI control value G is -100% or more, the limiter 166 outputs the PI control value G as it is as the limited PI control value GL. If the PI control value G is lower than -100%, the limiter 166 outputs -100% as the limited PI control value GL. The subtractor 168 constituting the charging limit gain calculation circuit subtracts the limited PI control value GL from the fixed value -100%, and outputs the difference as the charging limit gain. The charging limit gain is set as the lower limit value PreflimL of the variable limiter 122.

[0074] When the PI control value G is −600% as in the above-mentioned example during charging, the limited PI control value GL is −100%, and the lower limit value PreflimL is set to 0%. As a result, the power command value Pref that commands charging is limited to 0% by the variable limiter 122, and the power command value Pref2 limited to 0% is input to the drive signal generator 110.

[0075] <Second concrete example> 9 is a diagram showing a second specific example of the configuration of the control device 100. In the second specific example, the command value limiter 120 is composed of a variable limiter 122, similar to the first specific example. The variable limiter 122 outputs a power command value Pref2 that is limited by an upper limit value PreflimH or a lower limit value PreflimL for the power command value Pref.

[0076] In the second specific example, similarly to the first specific example, the voltage deviation calculator 140 includes a limiter 142 and a subtractor 144. If the measured DC voltage Vdcfbk is equal to or greater than the charge limiter operation voltage value VdclimH, the deviation Vdcerr between the charge limiter operation voltage value VdclimH and the measured DC voltage Vdcfbk is output from the subtractor 144. If the measured DC voltage Vdcfbk is equal to or less than the discharge limiter operation voltage value VdclimL, the deviation Vdcerr between the discharge limiter operation voltage value VdclimL and the measured DC voltage Vdcfbk is output from the subtractor 144.

[0077] In the second specific example, the PI controller 150 includes a PI controller 154 for discharging control and a PI controller 156 for charging control. The PI controller 154 and the PI controller 156 are connected to the subtractor 144 in parallel.

[0078] The PI controller 154 for discharge control has the configuration shown in the lower part of Fig. 3. The PI control value G1 for discharge limiting output from the PI controller 154 is calculated according to the above-mentioned formula (10). If the system lower limit voltage Vdcmin is 710V, the discharge limiter activation voltage value VdclimL is 720V, and if the deviation Vdcerr is 4V as in the above-mentioned example during discharge, then the PI control value G1 for discharge limiting is 0.6.

[0079] The PI controller 156 for charge control has the configuration shown in the upper part of Fig. 3. The PI control value G2 for charge limit output from the PI controller 156 is calculated according to the above-mentioned formula (9). If the system upper limit voltage Vdcmax is 1100V and the charge limiter activation voltage value VdclimH is 1090V, then if the deviation Vdcerr is -60V as in the above-mentioned example during charging, the PI control value G2 for charge limit is -5.

[0080] In the second specific example, the limiter adjuster 160 is composed of a discharge limit gain adjustment circuit made up of a limiter 172 and a multiplier 174, and a charge limit gain adjustment circuit made up of a limiter 176 and a multiplier 178. The discharge limit gain adjustment circuit is a circuit that adjusts the upper limit value PreflimH of the variable limiter 122 within the range of 100% to 0%. The charge limit gain adjustment circuit is a circuit that adjusts the lower limit value PreflimL of the variable limiter 122 within the range of -100% to 0%.

[0081] The limiter 172 constituting the discharge limit gain adjustment circuit limits the PI control value G1 for discharge limit calculated by the PI controller 154 to a range between 1 and 0, and outputs the limited PI control value GH. When the command from the higher-level device 4 is a discharge command, the PI control value G1 takes a value of 1 or less. If the PI control value G2 is 0 or more and 1 or less, the limiter 172 outputs the PI control value G1 as it is as the limited PI control value GH. If the PI control value G1 is lower than 0, the limiter 172 outputs 0 as the limited PI control value GH. The multiplier 174 constituting the discharge limit gain calculation circuit multiplies the limited PI control value GH by 100%, which is a fixed value, and outputs the product as the discharge limit gain. The discharge limit gain is set as the upper limit value PreflimH of the variable limiter 122.

[0082] When the PI control value G1 is 0.6 as in the above-mentioned example during discharging, the limited PI control value GH becomes 0.6, and the upper limit value PreflimH is set to 60%. As a result, the power command value Pref that commands discharging is limited to 60% by the variable limiter 122, and the power command value Pref2 limited to 60% is input to the drive signal generator 110.

[0083] The limiter 176 constituting the charging limit gain calculation circuit limits the PI control value G2 for charging limit calculated by the PI controller 156 to a range of 1 to 0, and outputs the limited PI control value GL. When the command from the higher-level device 4 is a charging command, the PI control value G2 takes a value of 1 or less. If the PI control value G2 is 0 or more and 1 or less, the limiter 176 outputs the PI control value G2 as it is as the limited PI control value GL. If the PI control value G2 is lower than 0, the limiter 176 outputs 0 as the limited PI control value GL. The multiplier 178 constituting the charging limit gain calculation circuit multiplies the limited PI control value GL by −100%, which is a fixed value, and outputs the product as the charging limit gain. The charging limit gain is set as the lower limit value PreflimL of the variable limiter 122.

[0084] When the PI control value G1 is −5 as in the above-mentioned example during charging, the limited PI control value GL becomes 0, and the lower limit value PreflimL is set to 0%. As a result, the power command value Pref that commands charging is limited to 0% by the variable limiter 122, and the power command value Pref2 limited to 0% is input to the drive signal generator 110.

[0085] <Third Specific Example> 10 is a diagram showing a third specific example of the configuration of the control device 100. In the third specific example, the command value limiter 120 is composed of a gain multiplier 124. The gain multiplier 124 multiplies the power command value Pref by a gain. A positive power command value Pref, i.e., a discharge power command value, is multiplied by a discharge limit gain in the range from 1 to 0. A negative power command value Pref, i.e., a charge power command value, is multiplied by a charge limit gain in the range from 1 to 0. The gain multiplier 124 outputs the power command value Pref multiplied by the discharge limit gain or the charge limit gain as a limited power command value Pref2.

[0086] In the third specific example, similarly to the first and second specific examples, the voltage deviation calculator 140 includes a limiter 142 and a subtractor 144. If the measured DC voltage Vdcfbk is equal to or greater than the charge limiter operating voltage value VdclimH, the subtractor 144 outputs the deviation Vdcerr between the charge limiter operating voltage value VdclimH and the measured DC voltage Vdcfbk. If the measured DC voltage Vdcfbk is equal to or less than the discharge limiter operating voltage value VdclimL, the subtractor 144 outputs the deviation Vdcerr between the discharge limiter operating voltage value VdclimL and the measured DC voltage Vdcfbk.

[0087] In the third specific example, similarly to the second specific example, the PI controller 150 is composed of a PI controller 154 for discharge control and a PI controller 156 for charge limit. The PI controller 154 for discharge control has the configuration shown in the lower part of Fig. 3, and outputs a PI control value G1 for discharge limit. The PI controller 156 for charge control has the configuration shown in the upper part of Fig. 3, and outputs a PI control value G2 for charge limit.

[0088] In the third specific example, the limiter adjuster 160 is composed of a limiter 182 for setting a discharge limiting gain, a limiter 184 for setting a charge limiting gain, a gain switch 186, and a switch determiner 188. The limiter adjuster 160 is a circuit that adjusts the discharge limiting gain and the charge limiting gain, which are multiplied by the power command value Pref in the gain multiplier 124, within the ranges of 1 to 0.

[0089] The limiter 182 for setting the discharge limit gain limits the PI control value G1 for discharge limit calculated by the PI controller 154 to within a range from 1 to 0, and outputs the limited PI control value as the discharge limit gain GH. When the command from the higher-level device 4 is a discharge command, the PI control value G1 takes a value of 1 or less. If the PI control value G1 is between 0 and 1, the limiter 182 outputs the PI control value G1 as is as the discharge limit gain GH. If the PI control value G1 is lower than 0, the limiter 182 outputs 0 as the limited discharge limit gain GH.

[0090] The limiter 184 for setting the charging limit gain limits the PI control value G2 for charging limit calculated by the PI controller 156 to within a range from 1 to 0, and outputs the limited PI control value as the charging limit gain GL. When the command from the higher-level device 4 is a charging command, the PI control value G2 takes a value of 1 or less. If the PI control value G2 is 0 or more and 1 or less, the limiter 184 outputs the PI control value G2 as it is as the charging limit gain GL. If the PI control value G2 is lower than 0, the limiter 184 outputs 0 as the limited charging limit gain GL.

[0091] The discharge limiting gain GH output from the limiter 182 and the charge limiting gain GL output from the limiter 184 are both input to a gain switch 186. The gain switch 186 switches the gain to be selected between the discharge limiting gain GH and the charge limiting gain GL in response to a trigger signal input from a switch determination unit 188. The gain selected by the gain switch 186 is input to the gain multiplier 124 and multiplied by the power command value Pref as the discharge limiting gain or the charge limiting gain.

[0092] The switching determinator 188 compares the power command value Pref with zero, which is a reference value, and inputs a trigger signal based on the comparison result to the gain switch 186. In response to the power command value Pref becoming equal to or greater than zero, the switching determinator 188 inputs a trigger signal to the gain switch 186 so that the discharge limiting gain GH input from the limiter 182 is selected. In addition, in response to the power command value Pref becoming zero, the switching determinator 188 inputs a trigger signal to the gain switch 186 so that the charge limiting gain GL input from the limiter 184 is selected.

[0093] During discharging, the power command value Pref is a positive value, so the gain switch 186 selects the discharge limit gain GH input from the limiter 182. As a result, the discharge limit gain GH is input to the gain multiplier 124. When the PI control value G1 calculated by the PI controller 154 is 0.6 as in the above-described example during discharging, the discharge limit gain GH becomes 0.6, and the gain multiplier 124 multiplies the power command value Pref by 0.5. As a result, a power command value Pref2 whose ratio to the power command value Pref is limited to 0.6 is input to the drive signal generator 110.

[0094] During charging, since the power command value Pref is a negative value, the gain switch 186 selects the charging limit gain GL input from the limiter 184. As a result, the charging limit gain GL is input to the gain multiplier 124. When the PI control value G2 calculated by the PI controller 156 is −5 as in the above-described example during charging, the charging limit gain GL becomes zero, and the gain multiplier 124 multiplies the power command value Pref by zero. As a result, the power command value Pref2, the ratio of which to the power command value Pref is limited to zero, is input to the drive signal generator 110.

[0095] 4.Effects As described above, according to the PCS 10 of this embodiment, it is possible to prevent overcharging and overdischarging of the storage battery 6 with a simple configuration as shown in the first to third specific examples. Moreover, the PCS 10 of this embodiment can be realized by changing only the software of the control device, without changing the hardware of a conventional PCS.

[0096] According to the PCS 10 of this embodiment, the limitation on the command value of the charging power by the command value limiter 120 is strengthened according to the PI control value for the deviation between the measured DC voltage and the charge limiter operating voltage. This makes it possible to suppress chattering of the command value limiter 120 caused by voltage fluctuations and continue the charging operation as long as possible. Also, according to the PCS 10 of this embodiment, the limitation on the command value of the discharging power by the command value limiter 120 is strengthened according to the PI control value for the deviation between the measured DC voltage and the discharge limiter operating voltage. This makes it possible to suppress chattering of the command value limiter 120 caused by voltage fluctuations and continue the discharging operation as long as possible. [Explanation of symbols]

[0097] 2. Power Conversion System 4. Upper device 6. Storage battery 10 Power conditioner 20 Inverter circuit 80 Voltmeter 100 Control device 110 Drive signal generator 120 Command value limiter 130 Voltage limit range setting device 140 Voltage deviation calculator 150 PI Controller 160 Limiter Adjuster

Claims

1. An inverter circuit that connects the AC power system and the storage battery; a command value limiter configured to limit a command value of charging power commanded from a higher-level device and a command value of discharging power commanded from the higher-level device; a drive signal generator configured to generate a drive signal for the inverter circuit according to the command value of the charging power limited by the command value limiter or the command value of the discharging power limited by the command value limiter; a PI controller configured to calculate a PI control value for charge limiting, which is a PI control value for a deviation between the DC voltage and the charge limiter operating voltage, when the DC voltage applied to the inverter circuit is higher than a predetermined charge limiter operating voltage, and to calculate a PI control value for discharge limiting, which is a PI control value for a deviation between the DC voltage and the discharge limiter operating voltage, when the DC voltage is lower than a predetermined discharge limiter operating voltage; a limiter adjuster configured to adjust a limit on the command value of the charging power by the command value limiter so as to reduce the magnitude of the command value of the charging power in accordance with the PI control value for limiting the charging, and to adjust a limit on the command value of the discharging power by the command value limiter so as to reduce the magnitude of the command value of the discharging power in accordance with the PI control value for limiting the discharging. The power conditioner is characterized by the above.

2. The power conditioner according to claim 1, the command value limiter is configured to multiply the command value of the charging power by a charge limit gain having a value of 0 or more and 1 or less, and to multiply the command value of the discharging power by a discharge limit gain having a value of 0 or more and 1 or less, The limiter adjuster is configured to reduce the charge limit gain in response to the PI control value for the charge limit and to reduce the discharge limit gain in response to the PI control value for the discharge limit. The power conditioner is characterized by the above.

3. The power conditioner according to claim 2, The limiter adjuster is configured to maintain the charge limit gain at zero while the PI control value for the charge limit is outside a predetermined range, and to maintain the discharge limit gain at zero while the PI control value for the discharge limit is outside a predetermined range. The power conditioner is characterized by the above.

4. An inverter circuit that connects the AC power system and the storage battery; a command value limiter configured to impose a limit on a command value of the charging power commanded from a higher-level device; a drive signal generator configured to generate a drive signal for the inverter circuit according to the command value of the charging power limited by the command value limiter; a PI controller configured to calculate a PI control value for a deviation between the DC voltage and the charge limiter operating voltage when the DC voltage applied to the inverter circuit is higher than a predetermined charge limiter operating voltage; a limiter adjuster configured to adjust a limit on the command value of the charging power by the command value limiter so as to reduce the magnitude of the command value of the charging power in response to the PI control value. The power conditioner is characterized by the above.

5. The power conditioner according to claim 4, the command value limiter is configured to multiply the command value of the charging power by a charging limit gain having a value not less than 0 and not more than 1; The limiter regulator is configured to reduce the charge limit gain in response to the PI control value. The power conditioner is characterized by the above.

6. The power conditioner according to claim 5, The limiter regulator is configured to maintain the charge limit gain at zero while the PI control value is outside a predetermined range. The power conditioner is characterized by the above.

7. An inverter circuit that connects the AC power system and the storage battery; a command value limiter configured to impose a limit on a command value of a discharge power commanded from a higher-level device; a drive signal generator configured to generate a drive signal for the inverter circuit in accordance with the command value of the discharge power limited by the command value limiter; a PI controller configured to calculate a PI control value for a deviation between the DC voltage and the discharge limiter operating voltage when the DC voltage applied to the inverter circuit is lower than a predetermined discharge limiter operating voltage; a limiter adjuster configured to adjust a limit on the command value of the discharge power by the command value limiter so as to reduce the magnitude of the command value of the discharge power in response to the PI control value. The power conditioner is characterized by the above.

8. The power conditioner according to claim 7, the command value limiter is configured to multiply the command value of the discharge power by a discharge limit gain having a value between 0 and 1, The limiter regulator is configured to reduce the discharge limit gain in response to the PI control value. The power conditioner is characterized by the above.

9. The power conditioner according to claim 8, The limiter regulator is configured to maintain the discharge limit gain at zero while the PI control value is outside a predetermined range. The power conditioner is characterized by the above.

10. One or more power conditioners connected to a common AC power grid; A host device that issues a command value of a charging power or a command value of a discharging power to the one or more power conditioners, Each of the one or more power conditioners is a power conditioner according to any one of claims 1 to 9. A power conversion system comprising:

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