Power conversion device and power storage system

Abstract

In the present invention, if, after a timer start signal is inputted from a microcontroller 40, a first set time elapses without a clear signal being inputted from the microcontroller 40, then a watchdog timer 50 outputs, to the microcontroller 40, an interrupt signal for starting up an interrupt handler for shutting down DC-DC converters 30a-30d in a normal procedure. If a second set time elapses after a timer start signal is inputted from the interrupt handler of the microcontroller 40, then the watchdog timer 50 outputs a reset signal to the microcontroller 40.

Description

Power Conversion Device and Battery Energy Storage System

[0001] The present disclosure relates to a power conversion device and a battery energy storage system for charging and discharging a storage battery.

[0002] A DC / DC converter is used to charge and discharge the storage battery. In a general DC / DC converter, feedback control using a microcontroller is performed. The microcontroller calculates the duty ratio of a PWM (Pulse Width Modulation) signal according to the error between the output voltage or output current and the target value so that the output voltage or output current maintains the target value. If an abnormality occurs in the control of the microcontroller, it becomes impossible to appropriately control the duty ratio of the PWM signal according to the load fluctuation, and abnormalities such as overcurrent and overvoltage may occur in the DC / DC converter.

[0003] A watchdog timer may be used as a means for monitoring whether the microcontroller is operating normally. The watchdog timer is a timer for monitoring whether an abnormality has occurred in the program executed by the microcontroller. When the watchdog timer detects that the microcontroller's program has run wild or stopped, it outputs a reset command to the microcontroller to stop and restart the program to prevent circuit failures.

[0004] Patent Document 1 discloses a method of changing the detection time of the watchdog timer in a power tool according to operations such as motor drive and battery charging and discharging, and shortening the time from the start of abnormal operation to detection when performing a process with a high risk of failure. In addition, by providing two watchdog timers, a method of reducing the circuit failure risk by the other watchdog timer stopping the circuit even if one watchdog timer stops operating normally is disclosed.

[0005] Patent Document 2 discloses a method of determining that a failure has occurred in a current detection resistor when a reset command of the watchdog timer is input and the current detection resistor of the power supply circuit is not detecting current.

[0006] Japanese Patent Publication No. 2014-155979 Japanese Patent Publication No. 2023-153697

[0007] When a watchdog timer reset command is used to forcibly stop the control of a microcontroller, depending on the timing at which the watchdog timer outputs the reset command, the circuit may not be able to be controlled properly, and there is a risk of circuit failure. For example, if the microcontroller program stops during charging or discharging by a DC / DC converter, signals controlled by something other than the software may cause abnormal operation of the DC / DC converter, and there is a risk of circuit failure due to overcurrent or overvoltage. In addition, when stopping the control of the microcontroller, the appropriate stopping method differs depending on the state of the DC / DC converter, so it is necessary to properly manage the state of the circuit. Furthermore, in a configuration in which failure determination is made based on multiple conditions, as shown in Patent Document 2, there are many constraints on the circuit configuration.

[0008] This disclosure is made in light of these circumstances, and its purpose is to provide a technology for safely stopping and restarting a DC / DC converter in the event of a malfunction in the control of a microcontroller.

[0009] To solve the above problems, a power conversion device according to one embodiment of the present disclosure comprises a DC / DC converter connected to a storage battery, a microcontroller that controls the DC / DC converter, and a watchdog timer that monitors whether the microcontroller is operating normally. The watchdog timer outputs an interrupt signal to the microcontroller to activate an interrupt handler for terminating the DC / DC converter in the proper procedure when a first set time has elapsed since the timer activation signal was input from the microcontroller without a clear signal being input from the microcontroller, and outputs a reset signal to the microcontroller when a second set time has elapsed since the timer activation signal was input from the interrupt handler of the microcontroller.

[0010] According to this disclosure, the DC / DC converter can be safely stopped and restarted in the event of a malfunction in the control of the microcontroller.

[0011] This is a diagram illustrating an example configuration of an energy storage system according to an embodiment. This is a sequence diagram showing an example of fail-safe processing using a watchdog timer according to a comparative example. This is a sequence diagram showing an example of fail-safe processing using a watchdog timer according to an embodiment.

[0012] Figure 1 is a diagram illustrating an example configuration of an energy storage system 1 according to an embodiment. The energy storage system 1 according to this embodiment is used as a power supply system for a data center. Load 3 is a collective term for a large number of servers and storage devices installed in the data center. Load 3 is connected to a DC bus 2. In this embodiment, a 48V DC bus 2 is assumed. An AC / DC converter 5 connected to a commercial power grid 4, an emergency generator 6, and the energy storage system 1 are connected to the DC bus 2.

[0013] The AC / DC converter 5 converts the AC power supplied from the commercial power grid 4 into DC power while stepping it down, and outputs it to the DC bus 2. For example, it converts the 200-240V AC voltage supplied from the commercial power grid 4 into 48V DC power.

[0014] The emergency generator 6 is a generator that supplies power to the load 3 in the event of a power outage in the commercial power grid 4, and can be a diesel generator or a gas turbine generator, for example. It takes several tens of seconds to several minutes from the time a power outage in the commercial power grid 4 is detected until the emergency generator 6 starts up. The energy storage system 1 can continue to supply backup power to the load 3 during that time.

[0015] The energy storage system 1 comprises a battery 10 and a power converter 20. The battery 10 includes a plurality of cells (for example, 9 to 14) connected in series. The cells can be lithium-ion battery cells, nickel-metal hydride battery cells, lead-acid battery cells, etc. Hereinafter, this specification assumes the use of lithium-ion battery cells (nominal voltage: 3.6-3.7V). In addition, multiple cells may be connected in parallel in the series stage of each cell in order to increase the capacity.

[0016] The power conversion device 20 comprises, as its main components, a plurality of (3 in the example shown in Figure 1) discharge DC / DC converters 30a-30c connected in parallel, a charge DC / DC converter 30d, a microcontroller 40, and a watchdog timer 50.

[0017] Multiple discharge DC / DC converters 30a-30c and a charging DC / DC converter 30d are connected between the battery 10 and the DC bus 2. The number of parallel discharge DC / DC converters 30a-30c is determined according to the power required by the load 3 during a power outage. Alternatively, a single discharge DC / DC converter with high current withstand capability may be used. The charging DC / DC converter 30d does not need to have high current withstand capability, as it only needs to charge the battery 10 at a low rate from the commercial power grid 4.

[0018] Switching type DC / DC converters are used for the discharge DC / DC converters 30a-30c and the charge DC / DC converter 30d. They may be isolated or non-isolated.

[0019] For example, the same non-isolated H-bridge buck-boost converter capable of both boosting and bucking voltage operation may be used for the multiple discharge DC / DC converters 30a-30c and the charging DC / DC converter 30d. In the case where the voltage of the storage battery 10 is always lower than the voltage of the DC bus 2, boost converters may be used for the multiple discharge DC / DC converters 30a-30c and a buck converter for the charging DC / DC converter 30d.

[0020] ORing circuits 31a-31c are connected between the outputs of the discharge DC / DC converters 30a-30c and the DC bus 2, respectively. ORing circuit 31d is connected between the output of the charge DC / DC converter 30d and the energy storage system 1. Ideal diode ICs can be used for ORing circuits 31a-31d, for example. An ideal diode IC is an IC that can allow current to flow in the forward direction with almost no loss while preventing reverse current. An ideal diode IC includes a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), and when the input voltage of the MOSFET drops by a predetermined value below the output voltage, the MOSFET turns off to prevent reverse current.

[0021] A hot-swap circuit 32 is connected between the charging DC / DC converter 30d and the DC bus 2. The hot-swap circuit 32 includes a current sensing resistor, a MOSFET, and a control IC. The control IC protects the power converter 20 by turning off the MOSFET when it detects abnormalities such as overcurrent, inrush current, short circuit, overvoltage, undervoltage, or reverse polarity connection. Although only one energy storage system 1 is shown in Figure 1, in reality, multiple unitized energy storage systems 1 are often connected in parallel to the DC bus 2. By providing the hot-swap circuit 32, each energy storage system 1 can be safely hot-swapped.

[0022] The microcontroller 40 controls the operation of multiple discharge DC / DC converters 30a-30c and a charge DC / DC converter 30d. Each of the multiple discharge DC / DC converters 30a-30c and the charge DC / DC converter 30d includes a gate driver IC.

[0023] When stepping down the voltage of a switching-type DC / DC converter, the ratio of the transmission mode, in which power is transmitted to the output side while charging the reactor from the input DC power supply, and the commutation mode, in which the connection between the input side and the reactor is blocked and only the power stored in the reactor is transmitted to the output side, is controlled by controlling the duty cycle of the switching element (e.g., MOSFET).

[0024] When a switching-type DC / DC converter is operated in a boost mode, the ratio of the storage mode, in which the reactor and output are shut off and the reactor is charged from the input DC power supply, to the transmission mode, in which power is transmitted from both the input DC power supply and the reactor to the output side, is controlled by controlling the duty cycle of the switching element.

[0025] The microcontroller 40 generates PWM signals to maintain the output voltages of the discharge DC / DC converters 30a-30c at the target voltage and outputs them to the respective gate driver ICs. The gate driver ICs generate gate voltages to drive the switching elements based on the PWM signals input from the microcontroller 40 and supply them to the gate terminals of the switching elements.

[0026] The microcontroller 40 generates a PWM signal to maintain the output current of the charging DC / DC converter 30d at a target current, or a PWM signal to maintain the output voltage of the charging DC / DC converter 30d at a target voltage, and outputs it to the gate driver IC. Based on the PWM signal input from the microcontroller 40, the gate driver IC generates a gate voltage to drive the switching element and supplies it to the gate terminal of the switching element.

[0027] The watchdog timer 50 monitors whether the microcontroller 40 is operating correctly. The watchdog timer 50 may be built into the same package as the microcontroller 40, or it may be installed outside the package of the microcontroller 40.

[0028] The watchdog timer 50 has a counter that starts counting up when a start signal is input from the microcontroller 40, and stops counting up when a clear signal is input from the microcontroller 40. If a clear signal is not input from the microcontroller 40 within a set time from the start of counting up, the counting up will not stop, and the counter will overflow. Counter overflow means that the microcontroller 40 is not functioning correctly.

[0029] Figure 2 is a sequence diagram showing an example of fail-safe processing using a watchdog timer 50 in a comparative example. The charge / discharge control program of the microcontroller 40 outputs a timer start signal (P1) to the watchdog timer 50. When the watchdog timer 50 receives the timer start signal from the microcontroller 40, it starts counting up.

[0030] The charge / discharge control program of the microcontroller 40 executes a discharge start process for the discharge DC / DC converters 30a-30c (P2). The discharge DC / DC converters 30a-30c perform power conversion according to the control signal from the microcontroller 40.

[0031] If the charge / discharge control program of the microcontroller 40 malfunctions for any reason, the microcontroller 40's charge / discharge control program will be unable to output a timer clear signal to the watchdog timer 50. Even if the charge / discharge control program of the microcontroller 40 malfunctions, the gate driver ICs of the discharge DC / DC converters 30a-30c will continue to operate. However, if the charge / discharge control program of the microcontroller 40 malfunctions, the feedback control will also malfunction. If the duty cycle of the PWM signal is fixed due to the malfunction of the feedback control, there is a risk of overcurrent or overvoltage occurring depending on fluctuations in the load 3. In addition, there is a risk that the control of the switching element may oscillate due to the malfunction of the feedback control.

[0032] The watchdog timer 50 overflows if a timer clear signal is not input after a set time (for example, 1 second) has elapsed since the start of counting up. When the counter overflows, the watchdog timer 50 outputs a reset signal to the microcontroller 40 (P3).

[0033] When the microcontroller 40 receives a reset signal from the watchdog timer 50, it restarts the charge / discharge control program (P4). After the charge / discharge control program of the microcontroller 40 restarts, it performs initialization processing for the discharge DC / DC converters 30a-30c and the charge DC / DC converter 30d (P5).

[0034] The charge / discharge control program of the microcontroller 40 performs initialization processes such as initializing the ports into which detected values ​​are input from the discharge DC / DC converters 30a-30c and the charge DC / DC converter 30d, initializing the ports that output PWM signals to the respective gate driver ICs of the discharge DC / DC converters 30a-30c and the charge DC / DC converter 30d, starting the ORing circuits 31a-31d, and notifying the Battery Management System (BMS) of the battery 10 to start up.

[0035] In the sequence shown in Figure 2, the discharge DC / DC converters 30a-30c are operating when the charge / discharge control program of the microcontroller 40 executes the initialization process for the discharge DC / DC converters 30a-30c. Even if the feedback control by the microcontroller 40 stops, the discharge DC / DC converters 30a-30c will continue to operate with a basically fixed duty cycle if the fluctuation of load 3 is small. If the initialization process is executed while the discharge DC / DC converters 30a-30c are operating, an unexpected signal may be input, potentially causing the circuit to fail.

[0036] Figure 3 is a sequence diagram showing an example of fail-safe processing using a watchdog timer 50 according to an embodiment. The charge / discharge control program of the microcontroller 40 outputs a timer start signal to the watchdog timer 50 (P11). When the watchdog timer 50 receives the timer start signal from the microcontroller 40, it starts counting up its counter.

[0037] The charge / discharge control program of the microcontroller 40 executes the charging start process of the charging DC / DC converter 30d (P12). The charging DC / DC converter 30d performs power conversion according to the control signal from the microcontroller 40. The microcontroller 40 stores "charging" as the operating state in its internal register (P13).

[0038] If the charge / discharge control program of the microcontroller 40 malfunctions for any reason, the charge / discharge control program of the microcontroller 40 will no longer be able to output a timer clear signal to the watchdog timer 50. Even if the charge / discharge control program of the microcontroller 40 malfunctions, the gate driver IC of the charging DC / DC converter 30d will continue to operate.

[0039] The watchdog timer 50 overflows if a first set time (for example, 1 second) elapses between the time the timer start signal is input from the microcontroller 40 and the time the timer clear signal is input from the microcontroller 40. Upon the first counter overflow, the watchdog timer 50 outputs an interrupt signal to the microcontroller 40 to activate the interrupt handler (P14).

[0040] When the microcontroller 40 receives an interrupt signal from the watchdog timer 50, it activates an interrupt handler to terminate the DC / DC converters 30a-30d in the proper procedure. When the interrupt handler of the microcontroller 40 is activated, it outputs a timer activation signal to the watchdog timer 50 (P15). Assuming that the abnormality in the charge / discharge control program is critical, the interrupt handler activates the watchdog timer 50 again.

[0041] The interrupt handler of the microcontroller 40 reads the operating status of the DC / DC converters 30a-30d from an internal register. The interrupt handler then executes termination processing according to the operating status. In the sequence shown in Figure 3, since the operating status is "charging," the interrupt handler of the microcontroller 40 executes the process to stop charging the charging DC / DC converter 30d (P16).

[0042] The interrupt handler of the microcontroller 40 performs the following actions as part of the normal termination procedure for the charging operation: issuing a stop command to the gate driver IC, turning off the ORing circuits 31a-31d, and notifying the battery 10 BMS of the end of charging. The interrupt handler stops when the termination process of the DC / DC converters 30a-30d is completed.

[0043] When the watchdog timer 50 receives a timer start signal from the interrupt handler of the microcontroller 40 and the second set time elapses, it overflows. When the watchdog timer 50 overflows for the second time, it outputs a reset signal to the microcontroller 40 (P17). The second set time only needs to be set to a time sufficient to normally complete the DC / DC converters 30a - 30d, and is set to a time shorter than the first set time. The second set time is set, for example, within 100 ms.

[0044] When the microcontroller 40 receives a reset signal from the watchdog timer 50, it restarts the charge / discharge control program (P18). When the charge / discharge control program of the microcontroller 40 restarts, it executes initialization processing for the discharge DC / DC converters 30a - 30c and the charge DC / DC converter 30d (P19). Since the charge DC / DC converter 30d has normally ended by the stop processing of P16, there is almost no risk of problems occurring due to the initialization processing.

[0045] As described above, according to the present embodiment, when the charge / discharge control program of the microcontroller 40 abnormally stops, the DC / DC converters 30a - 30d can be safely stopped and restarted. As a result, reset processing in a safe state becomes possible, and the risk of failure of the DC / DC converters 30a - 30d due to external factors other than software control can be reduced. Also, by setting the second set time shorter than the first set time, the time during which the power supply from the storage battery 10 to the load 3 stops can be minimized, and the reliability as a backup power supply can be ensured. In addition, since there is no need to add expensive hardware components, the fail-safe function can be enhanced at a low cost.

[0046] The above has been described based on the embodiments of the present disclosure. It is understood by those skilled in the art that the embodiments are examples, and various modifications are possible for the combination of each of their components and each processing process, and such modifications are also within the scope of the present disclosure.

[0047] In the above-described embodiment, the circuit configuration in which the discharge DC / DC converters 30a to 30c and the charge DC / DC converter 30d are provided separately has been described. However, a bidirectional DC / DC converter may be used to share the charging and discharging paths.

[0048] The power storage system 1 according to the present embodiment is applicable not only to backup use in a data center. For example, it is also applicable to a use in which power generated by a solar power generation system is charged and discharged to the commercial power system 4 at a predetermined timing. In that case, since it is not necessary to step down the voltage to 48V, the power storage system 1 that stores power at a voltage close to the voltage of the commercial power system 4 may be used.

[0049] The embodiment may also be specified by the following items.

[0050] [Item 1] Power conversion device (20) comprising: a DC / DC converter (30a-30d) connected to a storage battery (10); a microcontroller (40) that controls the DC / DC converter (30a-30d); and a watchdog timer (50) that monitors whether the microcontroller (40) is operating normally, wherein the watchdog timer (50) outputs an interrupt signal to the microcontroller (40) to activate an interrupt handler for terminating the DC / DC converter (30a-30d) in the proper procedure when a timer start signal is input from the microcontroller (40) and a clear signal is not input from the microcontroller (40) after a first set time has elapsed, and outputs a reset signal to the microcontroller (40) when a timer start signal is input from the interrupt handler of the microcontroller (40) and a second set time has elapsed. [Item 2] The power conversion device (20) according to Item 1, characterized in that the second setting time is set to a shorter time than the first setting time. This makes it possible to minimize the time during which charging or discharging is interrupted. [Item 3] The DC / DC converters (30a-30d) are connected between the storage battery (10) and the DC bus (2), and the DC bus (2) is connected to a load (3) to which backup power should be supplied and an AC / DC converter (5) connected to the commercial power grid (4), and the DC / DC converters (30a-30d) include a DC / DC converter (30d) for charging and a plurality of DC / DC converters (30a-30c) connected in parallel for discharging. This makes it possible to construct a highly reliable backup power supply. [Item 4] A power storage system (1) comprising a storage battery (10) and the power conversion device (20) according to any one of Items 1 to 3.According to this, if an abnormality occurs in the control of the microcontroller (40), the DC / DC converters (30a-30d) can be safely stopped and restarted.

[0051] This disclosure is applicable to a microcontroller that controls a DC / DC converter.

[0052] 1. Energy storage system, 2. DC bus, 3. Load, 4. Commercial power grid, 5. AC / DC converter, 6. Emergency generator, 10. Battery, 20. Power converter, 30a-30c. DC / DC converter for discharge, 30d. DC / DC converter for charging, 31a-31d. ORing circuit, 32. Hot-swap circuit, 40. Microcontroller, 50. Watchdog timer.

Claims

1. A power conversion device comprising: a DC / DC converter connected to a storage battery; a microcontroller that controls the DC / DC converter; and a watchdog timer that monitors whether the microcontroller is operating normally, wherein the watchdog timer outputs an interrupt signal to the microcontroller to activate an interrupt handler for terminating the DC / DC converter in the proper procedure when a first set time has elapsed since a timer activation signal was input from the microcontroller without a clear signal being input from the microcontroller; and outputs a reset signal to the microcontroller when a second set time has elapsed since a timer activation signal was input from the interrupt handler of the microcontroller.

2. The power conversion device according to claim 1, characterized in that the second setting time is set to a shorter time than the first setting time.

3. The power conversion device according to claim 1, wherein the DC / DC converter is connected between the storage battery and the DC bus, the DC bus is connected to a load to which backup power should be supplied and an AC / DC converter connected to the commercial power grid, and the DC / DC converter includes a DC / DC converter for charging and a plurality of DC / DC converters for discharging connected in parallel.

4. A storage system comprising a storage battery and a power conversion device according to any one of claims 1 to 3.

Images