JP7792867B2 - uninterruptible power supply - Google Patents

Description

This disclosure relates to an uninterruptible power supply that supplies power from an AC power source to a load and, in the event of an abnormality in the AC power source, supplies power from a power storage unit to the load.

An uninterruptible power supply includes a rectifier that converts AC to DC, an inverter that converts the DC back to AC, and a storage battery connected to a DC bus that connects the rectifier and inverter. The uninterruptible power supply shown in Patent Document 1 below further includes a series circuit consisting of a switch and resistor connected to the DC bus, and a switching command device that controls the opening and closing of the switch. Patent Document 1 discloses technology that controls the switch to the on state when the current flowing into the DC bus or the DC bus voltage exceeds a predetermined value, causing the resistor to consume regenerative power generated by the load.

Japanese Patent Application Publication No. 5-64378

The technology described in Patent Document 1 above can suppress increases in DC bus current and DC bus voltage caused by regenerative power generated by the load, preventing deterioration and damage to the storage battery and circuit components. However, the uninterruptible power supply described in Patent Document 1 has the drawback of wasting regenerative power and resulting in poor regeneration efficiency, as most of the regenerative power generated by the load is consumed by resistors.

The present disclosure has been made in light of the above, and aims to provide an uninterruptible power supply that can supply as much regenerative power generated by a load as possible to a storage battery, thereby increasing regenerative efficiency.

To solve the above-mentioned problems and achieve the objectives, the uninterruptible power supply according to the present disclosure is an uninterruptible power supply equipped with a power storage unit, and includes a first power conversion unit that converts power from an AC power source into DC power, a capacitor that is charged with DC power, and a second power conversion unit that converts the DC output of the capacitor into AC power and outputs it to a load. The uninterruptible power supply also includes a third power conversion unit that transfers charge from the capacitor to the power storage unit when the AC power source is healthy and transfers charge from the power storage unit to the capacitor when the AC power source is abnormal, and a voltage detection unit that detects the capacitor voltage. When the AC power source is abnormal and the capacitor voltage detected by the voltage detection unit is equal to or greater than a first value, the third power conversion unit transfers the charge of the capacitor to the power storage unit.

The uninterruptible power supply device disclosed herein can supply as much regenerative power generated by the load as possible to the storage battery, thereby achieving the effect of improving regeneration efficiency.

FIG. 1 is a block diagram showing the overall configuration of an uninterruptible power supply according to a first embodiment. FIG. 2 is a block diagram showing the configuration of a first power conversion unit provided in the uninterruptible power supply shown in FIG. 1 . FIG. 2 is a block diagram showing the configuration of a second power conversion unit provided in the uninterruptible power supply shown in FIG. 1 ; FIG. 2 is a block diagram showing the configuration of a third power conversion unit provided in the uninterruptible power supply shown in FIG. 1 . 5 is a flowchart illustrating the operation of the charge/discharge control unit shown in FIG. 4 when the AC power supply is normal. 5 is a flowchart illustrating the operation of the charge/discharge control unit shown in FIG. 4 during backup operation. A circuit diagram showing the overall configuration of an uninterruptible power supply according to a second embodiment. FIG. 1 is a first diagram illustrating a charging operation of a positive-side capacitor and a negative-side capacitor provided in an uninterruptible power supply according to a second embodiment when the AC power supply is normal; FIG. 2 is a second diagram illustrating a charging operation of a positive-side capacitor and a negative-side capacitor provided in an uninterruptible power supply according to a second embodiment when the AC power supply is normal; FIG. 3 is a third diagram illustrating a charging operation of a positive-side capacitor and a negative-side capacitor provided in an uninterruptible power supply according to the second embodiment when the AC power supply is normal; FIG. 4 is a fourth diagram illustrating a charging operation of the positive-side capacitor and the negative-side capacitor provided in the uninterruptible power supply according to the second embodiment when the AC power supply is normal. FIG. 1 is a first diagram illustrating a charging operation when an AC power supply is normal for a power storage unit provided in an uninterruptible power supply according to a second embodiment; FIG. 2 is a second diagram illustrating a charging operation when the AC power supply is normal for the power storage unit provided in the uninterruptible power supply according to the second embodiment; FIG. 1 is a first diagram illustrating a charging operation of a positive-side capacitor provided in an uninterruptible power supply according to a second embodiment when an abnormality occurs in an AC power supply. FIG. 2 is a second diagram illustrating a charging operation of a positive-side capacitor provided in an uninterruptible power supply according to a second embodiment when an abnormality occurs in an AC power supply. FIG. 1 is a first diagram illustrating a charging operation of a negative-side capacitor provided in an uninterruptible power supply according to a second embodiment when an abnormality occurs in an AC power supply. FIG. 2 is a second diagram illustrating a charging operation of a negative-side capacitor provided in an uninterruptible power supply according to a second embodiment when an abnormality occurs in an AC power supply. FIG. 1 is a first diagram illustrating an operation for eliminating imbalance when the voltage of the negative-side capacitor becomes high among the positive-side capacitor and the negative-side capacitor provided in the uninterruptible power supply according to the second embodiment. FIG. 2 is a second diagram illustrating an operation for eliminating imbalance when the voltage of the negative-side capacitor becomes high among the positive-side capacitor and the negative-side capacitor provided in the uninterruptible power supply according to the second embodiment. FIG. 1 is a first diagram illustrating an operation for eliminating imbalance when the voltage of the positive-side capacitor becomes high among the positive-side capacitor and the negative-side capacitor provided in the uninterruptible power supply according to the second embodiment. FIG. 2 is a second diagram illustrating an operation for eliminating imbalance when the voltage of the positive-side capacitor becomes high among the positive-side capacitor and the negative-side capacitor provided in the uninterruptible power supply according to the second embodiment. FIG. 1 is a block diagram showing an example of a hardware configuration for implementing the functions of a charge/discharge control unit according to a first embodiment and a control circuit according to a second embodiment. FIG. 10 is a block diagram showing another example of a hardware configuration for realizing the functions of the charge/discharge control unit according to the first embodiment and the control circuit according to the second embodiment.

Uninterruptible power supplies according to embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Note that hereinafter, no distinction will be made between physical and electrical connections, and the term "connection" will be used. In other words, the term "connection" encompasses both direct connections between components and indirect connections between components via other components. Furthermore, the numerical values used below for voltage, current, time, ratios, etc. are merely examples, and the scope of the present disclosure is not limited by these examples.

Embodiment 1.
Fig. 1 is a block diagram showing the overall configuration of an uninterruptible power supply 100 according to embodiment 1. Fig. 2 is a block diagram showing the configuration of a first power conversion unit 2 provided in the uninterruptible power supply 100 shown in Fig. 1. Fig. 3 is a block diagram showing the configuration of a second power conversion unit 5 provided in the uninterruptible power supply 100 shown in Fig. 1. Fig. 4 is a block diagram showing the configuration of a third power conversion unit 7 provided in the uninterruptible power supply 100 shown in Fig. 1.

The uninterruptible power supply 100 is a power supply designed to ensure the operation of a powered device (load 4) and protect data by continuing to supply power for a certain period of time in the event of an abnormality in the AC power supply 1, such as a power outage or voltage drop. Specifically, the uninterruptible power supply 100 supplies power from the AC power supply 1 to the load 4, and in the event of an abnormality in the AC power supply 1, it can convert DC power stored in the power storage unit 6 to AC power and supply it to the load 4. To achieve this function, the uninterruptible power supply 100 according to the first embodiment includes a first power conversion unit 2, a capacitor 3, a second power conversion unit 5, a power storage unit 6, a third power conversion unit 7, a capacitor voltage detection unit 8, a setting unit 9, an output voltage detection unit 10, a current detection unit 11, and a regeneration detection unit 12, as shown in FIG. 1 .

The first power conversion unit 2 is connected to the AC power source 1 and converts the power of the AC power source 1 into DC power. The capacitor 3 is charged to a preset value, for example, 200 V, using the DC power supplied by the first power conversion unit 2. The second power conversion unit 5 is connected to the capacitor 3 and converts the DC output of the capacitor 3 into AC power and outputs it to the load 4. The second power conversion unit 5 converts the DC voltage, for example, 200 V, output from the capacitor 3 into an AC voltage, for example, 100 V. The power storage unit 6 supplies power to the second power conversion unit 5 so that it can continue to output AC power to the load 4 in the event of an abnormality in the AC power source 1. The third power conversion unit 7 is connected to the power storage unit 6 and charges the power storage unit 6 with power from the AC power source 1 when the AC power source 1 is operating normally and not abnormal. Furthermore, when an abnormality occurs in the AC power supply 1, the third power conversion unit 7 discharges power from the power storage unit 6 to supply power to the capacitor 3 and the second power conversion unit 5.

The capacitor voltage detection unit 8 detects the capacitor voltage, which is the voltage of the capacitor 3, and outputs the detected value to the third power conversion unit 7. The setting unit 9 sets whether the load 4 will perform regeneration and outputs this setting information to the third power conversion unit 7. The output voltage detection unit 10 detects the output voltage of the second power conversion unit 5 and outputs this detected value to the regeneration detection unit 12. The current detection unit 11 detects the current flowing between the second power conversion unit 5 and the load 4 and outputs this detected value to the regeneration detection unit 12. The regeneration detection unit 12 detects whether the load 4 is performing regeneration or power running based on the detection values of the output voltage detection unit 10 and the current detection unit 11, and outputs this operating information to the third power conversion unit 7.

As shown in Figure 2, the first power conversion unit 2 includes a bridge rectifier circuit 2a having four diodes, and a boost circuit 2b having a coil, a switching element, and a diode. The bridge rectifier circuit 2a rectifies the AC power from the AC power source 1 into DC power and outputs the rectified DC power to the boost circuit 2b. The boost circuit 2b boosts the voltage of the DC power and charges the capacitor voltage to a predetermined voltage. An example of the predetermined voltage is the aforementioned DC (Direct Current) 200V. Note that if the capacitor voltage rises above a predetermined threshold voltage, charging of the capacitor 3 is not performed.

As shown in FIG. 3, the second power conversion unit 5 includes a single-phase full-bridge inverter 5f having multiple self-extinguishing semiconductor switching elements 5a, 5b, 5c, and 5d with diodes connected in antiparallel, and a filter circuit 5e having a coil and a capacitor. An example of the self-extinguishing semiconductor switching elements 5a, 5b, 5c, and 5d is a metal-oxide-semiconductor field-effect transistor (MOSFET). Note that instead of MOSFETs, self-extinguishing semiconductor switching elements such as an insulated gate bipolar transistor (IGBT), a gate commutated turn-off thyristor (GCT), a gate turn-off thyristor (GTO), or a bipolar transistor may also be used. Furthermore, if the single-phase full-bridge inverter 5f has a circuit configuration capable of forced commutation operation, a thyristor without a self-extinguishing function may also be used. The single-phase full-bridge inverter 5f may also be configured as a half-bridge inverter by providing two DC-side capacitors, one for the positive side and one for the negative side.

As shown in FIG. 4, the third power conversion unit 7 includes a reactor 7a, self-extinguishing semiconductor switching elements 7b and 7c, a charge/discharge control unit 7d, and a voltage sensor 7e. The reactor 7a is connected to the positive electrode of the power storage unit 6. The self-extinguishing semiconductor switching element 7b is connected in parallel to the power storage unit 6 on the output side of the reactor 7a, i.e., on the side opposite the reactor 7a to which the power storage unit 6 is connected. The self-extinguishing semiconductor switching element 7c is connected between the reactor 7a and the positive electrode of the capacitor 3. While the self-extinguishing semiconductor switching elements 7b and 7c are MOSFETs as shown in the figure, they may also be self-extinguishing semiconductor switching elements such as IGBTs, GCTs, GTOs, and bipolar transistors. Furthermore, if the third power conversion unit 7 has a circuit configuration capable of forced commutation, a thyristor without a self-extinguishing function may also be used.

The charge/discharge control unit 7d controls the switching of the self-extinguishing semiconductor switching element 7b to boost the voltage of the storage unit 6, and controls the switching of the self-extinguishing semiconductor switching element 7c to charge the storage unit 6 via the reactor 7a. The voltage sensor 7e is connected to both ends of the storage unit 6, measures the voltage of the storage unit 6, and outputs the measured voltage signal to the charge/discharge control unit 7d. The charge/discharge control unit 7d also receives the output signal of the capacitor voltage detection unit 8, the output signal of the setting unit 9, and the output signal of the regeneration detection unit 12. The output signal of the capacitor voltage detection unit 8 contains information related to the detected capacitor voltage. The output signal of the setting unit 9 contains setting information indicating whether the load 4 is performing regeneration. The output signal of the regeneration detection unit 12 contains the aforementioned operating information, and this operating information includes information indicating whether the load 4 is performing regeneration or powering operation.

Next, the operation of the uninterruptible power supply 100 according to the first embodiment will be described. First, when the AC power supply 1 is operating normally, the first power conversion unit 2 converts the applied AC voltage of the AC power supply 1 to a DC voltage using the bridge rectifier circuit 2a, and then boosts the converted DC voltage using the boost circuit 2b to charge the capacitor 3 to a predetermined voltage of 200V DC. In this document, the AC power supply 1 operating normally refers to the AC voltage output by the AC power supply 1 being within the voltage range acceptable to the load 4. Hereinafter, the voltage range acceptable to the load 4 will be referred to as the "acceptable voltage range." If the rated voltage of the uninterruptible power supply 100 is, for example, 100V AC (alternate current), an example of the acceptable voltage range is 90V AC to 110V AC.

The second power conversion unit 5 converts the DC voltage of the capacitor 3 into a predetermined AC voltage and applies the converted AC voltage to the load 4. An example of the predetermined AC voltage is the above-mentioned AC 100V.

The third power conversion unit 7 has a constant current charging function that charges the power storage unit 6 with a predetermined constant current. An example of the predetermined constant current is 1 A. The voltage sensor 7e measures the voltage of the power storage unit 6. The third power conversion unit 7 uses the measurement value of the voltage sensor 7e to switch from constant current charging to constant voltage charging when the voltage of the power storage unit 6 reaches a predetermined voltage. Constant voltage charging is a charging method in which a constant voltage is applied to the power storage unit 6 to charge it. The third power conversion unit 7 is assumed to have a charging rate calculation unit that calculates the charging rate of the power storage unit 6 using a well-known method using the voltage of the power storage unit 6, etc.

As mentioned above, the setting unit 9 sets whether the load 4 will perform regeneration and outputs this setting information to the third power conversion unit 7. If the load 4 is a regenerative load, as described below, the charging rate of the power storage unit 6 is not increased to 100% even if the AC power supply 1 is healthy. On the other hand, if the load 4 is a non-regenerative load, the charging rate of the power storage unit 6 is increased to 100%. It is also possible to set the upper limit of the charging rate of the power storage unit 6 without providing the setting unit 9, based on the operating information output by the regeneration detection unit 12, i.e., information on whether the load 4 is performing regenerative operation or power running.

Next, detailed operation of the third power conversion unit 7 when the AC power supply 1 is healthy will be described with reference to Figure 5. Figure 5 is a flowchart illustrating operation of the charge/discharge control unit 7d shown in Figure 4 when the AC power supply 1 is healthy.

First, in step S101, the charging rate calculation unit calculates the charging rate of the power storage unit 6. In the next step S102, the regeneration detection unit 12 determines whether or not regenerative power from the load 4 is being detected. If regeneration is present (step S102, Yes), the process proceeds to step S104. If regeneration is not present (step S102, No), the process proceeds to step S103.

In step S103, it is determined whether the charging rate of the storage unit 6 calculated in step S101 is equal to or greater than a first threshold. The first threshold is set to, for example, 70%. If the charging rate of the storage unit 6 is equal to or greater than the first threshold (step S103, Yes), the process proceeds to step S105. If the charging rate is less than the first threshold (step S103, No), the process proceeds to step S106.

In step S105, discharge from the power storage unit 6 to the capacitor 3 begins, and the processing flow in Figure 5 ends.

In step S105, there is no regeneration from the load 4 and the charge rate is equal to or greater than the first threshold. Therefore, in step S105, the power storage unit 6 is discharged to lower the charge rate of the power storage unit 6. This allows the power storage unit 6 to be charged with the regenerated power when there is regeneration from the load 4.

In step S106, it is determined whether the charging rate is less than a second threshold. The second threshold is a value smaller than the first threshold, and is set to, for example, 50%. If the charging rate is less than the second threshold (step S106, Yes), proceed to step S107. If the charging rate is equal to or greater than the second threshold (step S106, No), proceed to step S108.

Step S107 is a state in which there is no regeneration from the load 4 and the charging rate is less than the second threshold. In other words, step S107 is a state in which the charging rate of the power storage unit 6 is sufficiently low, so charging of the power storage unit 6 begins and the processing flow in Figure 5 ends.

Step S108 is a state in which there is no regeneration from the load 4 and the charging rate is equal to or greater than the second threshold. In other words, step S108 is a state in which, if regeneration occurs, the regenerated power can be charged to the power storage unit 6, so charging and discharging of the power storage unit 6 is stopped and the processing flow in Figure 5 ends.

In step S104, it is determined whether the charging rate is less than 100%. If the charging rate is less than 100% (step S104, Yes), proceed to step S109; if the charging rate is 100% (step S104, No), proceed to step S110.

Step S109 is a state in which regeneration is occurring from load 4 and the charge rate is less than 100%. In other words, in step S109, the power storage unit 6 is not fully charged, so charging is performed from capacitor 3 to power storage unit 6. As a result, the charge in capacitor 3 is transferred to power storage unit 6, allowing capacitor 3 to receive regenerative power from load 4, making effective use of the regenerative power.

Step S110 is a state in which regeneration is occurring from the load 4 and the charging rate is 100%. In other words, step S110 is a state in which the regenerative power from the load 4 cannot be further charged to the power storage unit 6, so charging is stopped.

The processing flow shown in Figure 5 is executed at preset intervals. The preset interval is set to, for example, 10 ms.

The uninterruptible power supply 100 according to the first embodiment executes the processing flow shown in FIG. 5 while carrying out control according to the state of the AC power supply 1. Specifically, if the voltage of the AC power supply 1 drops below, for example, 90 V AC, which is the lower limit of the allowable voltage range, the uninterruptible power supply 100 determines that the AC power supply 1 has entered an abnormal state. In this case, the uninterruptible power supply 100 supplies power from the power storage unit 6 to the capacitor 3 via the third power conversion unit 7, and controls the capacitor 3 to maintain a predetermined voltage of 200 V DC. The uninterruptible power supply 100 also determines that the AC power supply 1 has entered an abnormal state if the voltage of the AC power supply 1 exceeds 110 V AC, which is the upper limit of the allowable voltage range, or if the capacitor voltage drops below, for example, 160 V, which is the lower limit of the predetermined voltage range.

Furthermore, in the event of an abnormality in the AC power supply 1, the second power conversion unit 5 continues to output an AC voltage of 100 V to the load 4. In this document, this operation is referred to as "backup operation." Backup operation continues until the voltage of the power storage unit 6 reaches a predetermined lower limit, for example, DC 50 V. Furthermore, if the voltage of the power storage unit 6 falls below DC 50 V, it is assumed that the stored energy in the power storage unit 6 has been depleted, and power supply to the load 4 is stopped.

Next, detailed operation of the third power conversion unit 7 during backup operation when an abnormality occurs in the AC power supply 1 will be described with reference to Figure 6. Figure 6 is a flowchart illustrating operation during backup operation in the charge/discharge control unit 7d shown in Figure 4.

First, in step S201, the capacitor voltage is obtained from the capacitor voltage detection unit 8. In the next step S202, it is determined whether the voltage value obtained in step S201 is equal to or greater than a first value. The first value is a set value, and is set to DC 215 V, for example. If the voltage value is equal to or greater than the first value (step S202, Yes), the process proceeds to step S203. If the voltage value is less than the first value (step S202, No), the process proceeds to step S204.

In step S203, although backup operation is in progress, regeneration from load 4 is occurring and the capacitor voltage is equal to or greater than the first value. Therefore, in order to make effective use of the regenerative power, charging from capacitor 3 to power storage unit 6 begins, and the process proceeds to step S206. Note that the charge in capacitor 3 is transferred to power storage unit 6 as a result of the processing in step S203.

In step S206, the charging rate of the power storage unit 6 is calculated, and the process proceeds to step S207.

In step S207, it is determined whether the charging rate is less than 100%. If the charging rate is less than 100% (step S207, Yes), the processing flow in Figure 6 ends. If the charging rate is not less than 100%, i.e., if the charging rate is 100% (step S207, No), the process proceeds to step S208.

Step S208 indicates a state in which, during backup operation, charging of the power storage unit 6 begins when the voltage of the capacitor 3 exceeds the first value due to regenerative power from the load 4, and charging then progresses until the charge rate of the power storage unit 6 reaches 100%. Therefore, further charging of the power storage unit 6 is no longer possible, so charging of the power storage unit 6 is stopped.

In step S204, it is determined whether the voltage value acquired in step S201 is less than a second value. The second value is a set value smaller than the first value, and is set to DC 200 V, for example. If the voltage value is less than the second value (step S204, Yes), the process proceeds to step S205. If the voltage value is equal to or greater than the second value (step S204, No), the process flow in Figure 6 ends.

In step S205, the capacitor voltage is in a low state. Therefore, in step S205, discharge from the power storage unit 6 to the capacitor 3 begins. As a result, the charge in the power storage unit 6 moves to the capacitor 3.

The processing flow shown in Figure 6 is executed at preset intervals. The preset interval is set to, for example, 10 ms.

As described above, in the uninterruptible power supply according to embodiment 1, the third power conversion unit operates to transfer charge from the capacitor to the storage unit when the AC power supply is healthy, and to transfer charge from the storage unit to the capacitor when the AC power supply is abnormal. Meanwhile, when the AC power supply is abnormal, the third power conversion unit operates to transfer charge from the capacitor to the storage unit if the capacitor voltage detected by the capacitor voltage detection unit is equal to or greater than the first value. This operation enables the capacitor to be in a state where it can accept regenerated power when regenerated from the load. This allows the regenerated power of the load to be used effectively.

Furthermore, in the uninterruptible power supply according to embodiment 1, when an abnormality occurs in the AC power supply and the capacitor voltage detected by the capacitor voltage detection unit falls below a second value that is smaller than the first value, the third power conversion unit operates to transfer charge from the power storage unit to the capacitor. This allows for uninterrupted power supply to the load even when the load switches from regenerative operation to power running.

The uninterruptible power supply according to embodiment 1 can also be configured to include a regeneration detection unit that detects the presence or absence of regenerative power from the load, and a charging rate calculation unit that calculates the charging rate of the power storage unit. In an uninterruptible power supply with this configuration, the third power conversion unit operates to transfer charge from the power storage unit to the capacitor when the AC power supply is healthy, the regeneration detection unit does not detect regenerative power, and the charging rate is equal to or greater than the first threshold. By transferring charge from the power storage unit to the capacitor, the charging rate of the power storage unit can be lowered. Furthermore, by lowering the charging rate of the power storage unit, when regeneration occurs from the load, the regenerative power of the load can be charged to the power storage unit. This allows the regenerative power of the load to be used effectively.

Furthermore, in the uninterruptible power supply according to embodiment 1, the third power conversion unit operates to transfer charge from the capacitor to the power storage unit when the AC power supply is healthy, the regeneration detection unit detects regenerative power, and the charge rate is less than 100%. This allows for a larger power capacity when accepting regenerative power from the load.

Embodiment 2.
7 is a circuit diagram showing the overall configuration of an uninterruptible power supply 101 according to embodiment 2. In the uninterruptible power supply 101 according to embodiment 2, the capacitor 3 in the uninterruptible power supply 100 according to embodiment 1 is configured with a positive-side capacitor 24a and a negative-side capacitor 24b. The uninterruptible power supply 101 according to embodiment 2 configured in this manner has the same functions as the uninterruptible power supply 101 according to embodiment 1. In addition, a balancing unit 25 is added to the uninterruptible power supply 101 according to embodiment 2 in order to transfer charge between the positive-side capacitor 24a and the negative-side capacitor 24b.

In FIG. 7, the uninterruptible power supply 101 according to the second embodiment includes first and second reverse current prevention diodes 21 and 22, an inverter unit 24, the aforementioned balancing unit 25, a negative pole step-up/step-down unit 26, and a converter unit 27. The first and second reverse current prevention diodes 21 and 22 and the converter unit 27 correspond to the "first power conversion unit 2" in the first embodiment, the inverter unit 24 corresponds to the "second power conversion unit 5" in the first embodiment, and the negative pole step-up/step-down unit 26 and the converter unit 27 correspond to the "third power conversion unit 7" in the first embodiment. Furthermore, in the second embodiment, the balancing unit 25 constitutes the "fourth power conversion unit."

In the uninterruptible power supply 101 according to embodiment 2, the balancing unit 25 transfers charge between the positive-side capacitor 24a and the negative-side capacitor 24b. Furthermore, the negative-side step-up/step-down unit 26 transfers charge from the negative-side capacitor 24b to the storage unit 6 when the AC power supply 1 is operating normally. On the other hand, when an abnormality occurs in the AC power supply 1, the negative-side step-up/step-down unit 26 transfers charge from the storage unit 6 to the negative-side capacitor 24b. Furthermore, when an abnormality occurs in the AC power supply 1, the converter unit 27 transfers charge from the storage unit 6 to the positive-side capacitor 24a.

Next, the layout, connections, and basic functions of each component will be described with reference to Figure 7. Components that are the same as or equivalent to those in embodiment 1 will be denoted by the same reference numerals, and overlapping descriptions will be omitted where appropriate.

The uninterruptible power supply 101 includes a common line 41 connecting one end of the AC power supply 1 to one end of the load 4, a positive voltage line 42 serving as the positive side of the DC, and a negative voltage line 43 serving as the negative side of the DC. The first and second reverse current prevention diodes 21, 22 are connected in series with the same polarity, and a connection point 44 of this series connection is connected to the other end of the AC power supply 1. The cathode of the first reverse current prevention diode 21 is connected to the positive voltage line 42, and the anode of the first reverse current prevention diode 21 is connected to the connection point 44. The anode of the second reverse current prevention diode 22 is connected to the negative voltage line 43, and the cathode of the second reverse current prevention diode 22 is connected to the connection point 44. The negative side of the storage unit 6 is connected to the common line 41.

A capacitor 28, a reactor 29, an AC power supply/battery selector switch 30, and a battery operation switch 31 are provided between the AC power supply 1 and the converter unit 27. The capacitor 28 is connected in parallel with the AC power supply 1 on the AC power supply 1 side. The reactor 29 is connected between the capacitor 28 and the converter unit 27 and forms a filter together with the capacitor 28. The AC power supply/battery selector switch 30 is connected between the capacitor 28 and the reactor 29 and switches the input between the AC power supply 1 and the power storage unit 6. Contact a of the AC power supply/battery selector switch 30 is connected to the AC power supply 1, and contact c of the AC power supply/battery selector switch 30 is connected to the reactor 29. The battery operation switch 31 is connected between contact b of the AC power supply/battery selector switch 30 and the positive side of the power storage unit 6.

In addition, a reactor 32 and a capacitor 33 are provided between the inverter unit 24 and the load 4. The reactor 32 is arranged on the output line 45 of the inverter unit 24, and the capacitor 33 is connected in parallel with the load 4 on the load 4 side of the reactor 32, forming a filter together with the reactor 32.

In addition to the positive side capacitor 24a and negative side capacitor 24b described above, the inverter unit 24 includes an inverter unit first semiconductor switch 24c, an inverter unit second semiconductor switch 24e, an inverter unit diode 24d, and an inverter unit diode 24f. The positive side capacitor 24a is connected between the common line 41 and the positive side voltage line 42, and the negative side capacitor 24b is connected between the common line 41 and the negative side voltage line 43. The inverter unit first semiconductor switch 24c has a collector connected to the positive side voltage line 42 and an emitter connected to the output line 45 via the reactor 32. The inverter unit second semiconductor switch 24e has a collector connected to the emitter of the inverter unit first semiconductor switch 24c and an emitter connected to the negative side voltage line 43. Inverter section diode 24d is connected in anti-parallel to inverter section first semiconductor switch 24c, and inverter section diode 24f is connected in anti-parallel to inverter section second semiconductor switch 24e.

The balancing unit 25 includes a balancing unit first semiconductor switch 25a, a balancing unit first diode 25b, a balancing unit second semiconductor switch 25c, a balancing unit second diode 25d, and a balancing unit reactor 25e. The balancing unit first semiconductor switch 25a has a collector connected to the positive voltage line 42 and an emitter connected to one end of the balancing unit reactor 25e. The other end of the balancing unit reactor 25e is connected to the common line 41. The balancing unit second semiconductor switch 25c has a collector connected to the emitter of the balancing unit first semiconductor switch 25a and an emitter connected to the negative voltage line 43. The balancing unit first diode 25b is connected in anti-parallel to the balancing unit first semiconductor switch 25a, and the balancing unit second diode 25d is connected in anti-parallel to the balancing unit second semiconductor switch 25c.

The negative voltage step-up/step-down unit 26 comprises a negative voltage step-up/step-down unit first semiconductor switch 26a, a negative voltage step-up/step-down unit first diode 26b, a negative voltage step-up/step-down unit reactor 26c, a negative voltage step-up/step-down unit second semiconductor switch 26d, and a negative voltage step-up/step-down unit second diode 26e. The collector of the negative voltage step-up/step-down unit first semiconductor switch 26a is connected to the positive side of the power storage unit 6, and the emitter is connected to one end of the negative voltage step-up/step-down unit reactor 26c. The other end of the negative voltage step-up/step-down unit reactor 26c is connected to the common line 41. The collector of the negative voltage step-up/step-down unit second semiconductor switch 26d is connected to the emitter of the negative voltage step-up/step-down unit first semiconductor switch 26a, and the emitter is connected to the negative voltage line 43. The negative side step-up/step-down section's first diode 26b is connected in anti-parallel to the negative side step-up/step-down section's first semiconductor switch 26a, and the negative side step-up/step-down section's second diode 26e is connected in anti-parallel to the negative side step-up/step-down section's second semiconductor switch 26d.

The converter section 27 includes diodes 27a1, 27a2, 27a3, and 27a4 that form a diode bridge 27a, and a converter section semiconductor switch 27b that is connected in parallel with the diode bridge 27a.

The uninterruptible power supply 101 further includes a capacitor voltage detection unit 34 and a control circuit 35. The capacitor voltage detection unit 34 detects the voltage of the positive-side capacitor 24a and the voltage of the negative-side capacitor 24b. The control circuit 35 controls the AC power supply/battery selector switch 30, the battery operation switch 31, the converter unit semiconductor switch 27b, the balancing unit first semiconductor switch 25a, the balancing unit second semiconductor switch 25c, the negative-side step-up/step-down unit first semiconductor switch 26a, and the negative-side step-up/step-down unit second semiconductor switch 26d. Although not shown, the control circuit 35 also controls the inverter unit first semiconductor switch 24c and the inverter unit second semiconductor switch 24e.

Here, the basic operation of the uninterruptible power supply 101 according to embodiment 2 will be described. First, in the uninterruptible power supply 101, the positive-side capacitor 24a and the negative-side capacitor 24b are charged by the AC power supply 1 when the AC power supply 1 is operating normally, and are charged by the storage unit 6 when the AC power supply 1 is malfunctioning. Furthermore, when the AC power supply 1 is operating normally and when an abnormality occurs, the inverter unit 24 converts the DC power output from the DC power supply into AC power using the positive-side capacitor 24a and the negative-side capacitor 24b as DC power sources, and supplies the converted AC power to the load 4. The negative-side step-up/step-down unit 26 transfers charge from the negative-side capacitor 24b to the storage unit 6 when the AC power supply 1 is operating normally, and transfers charge from the storage unit 6 to the negative-side capacitor 24b when the AC power supply 1 is malfunctioning. Furthermore, the converter unit 27 transfers charge from the storage unit 6 to the positive-side capacitor 24a when the AC power supply 1 is malfunctioning.

Next, the charging operation of the positive side capacitor 24a and the negative side capacitor 24b when the AC power supply 1 is operating normally will be described with reference to Figures 8 to 11. Figures 8 to 11 are first to fourth diagrams used to explain the charging operation of the positive side capacitor 24a and the negative side capacitor 24b provided in the uninterruptible power supply 101 according to embodiment 2 when the AC power supply 1 is operating normally. Note that in Figure 7, when the potential at one end of the AC power supply 1 is higher than the potential at the other end of the AC power supply 1, this is referred to as "the voltage of the AC power supply 1 is positive," and conversely, when the potential at one end of the AC power supply 1 is lower than the potential at the other end of the AC power supply 1, this is referred to as "the voltage of the AC power supply 1 is negative."

First, when the AC power supply 1 is healthy, the contact of the AC power supply/battery selector switch 30 is switched to contact a. Then, when the voltage of the AC power supply 1 is positive, as shown in Figure 8, the converter section semiconductor switch 27b is controlled to be ON. At this time, current flows from the AC power supply 1 → AC power supply/battery selector switch 30 → reactor 29 → diode 27a1 → converter section semiconductor switch 27b → diode 27a4 → AC power supply 1, and energy is stored in the reactor 29. Next, the converter section semiconductor switch 27b is controlled to be OFF. At this time, as shown in Figure 9, current flows from the reactor 29 → first reverse current prevention diode 21 → positive side capacitor 24a → AC power supply 1 → AC power supply/battery selector switch 30 → reactor 29, and the positive side capacitor 24a is charged with the energy stored in the reactor 29. Furthermore, if the voltage of the positive side capacitor 24a reaches or exceeds a predetermined value due to regenerative power from the load 4, charging by the converter unit 27 will be stopped or will not be performed.

When the voltage of AC power supply 1 is negative, as shown in FIG. 10, converter unit semiconductor switch 27b is turned on. At this time, current flows from AC power supply 1 to diode 27a2 to converter unit semiconductor switch 27b to diode 27a3 to reactor 29 to AC power supply/battery selector switch 30 to AC power supply 1, and energy is stored in reactor 29. Next, converter unit semiconductor switch 27b is turned off. At this time, as shown in FIG. 11, current flows from reactor 29 to AC power supply/battery selector switch 30 to AC power supply 1 to negative-side capacitor 24b to second reverse-flow prevention diode 22 to reactor 29, and negative-side capacitor 24b is charged with the energy stored in reactor 29. If the voltage of negative-side capacitor 24b reaches or exceeds a predetermined value due to regenerative power from load 4, charging by converter unit 27 is stopped or not performed.

Next, the charging operation of the power storage unit 6 when the AC power supply 1 is operating normally will be described with reference to Figures 12 and 13. Figures 12 and 13 are first and second diagrams, respectively, used to explain the charging operation of the power storage unit 6 provided in the uninterruptible power supply 101 according to embodiment 2 when the AC power supply 1 is operating normally.

First, as shown in FIG. 12, the negative side step-up/step-down unit second semiconductor switch 26d is turned on. At this time, current flows from the negative side capacitor 24b → negative side step-up/step-down unit reactor 26c → negative side step-up/step-down unit second semiconductor switch 26d → negative side capacitor 24b, and energy is stored in the negative side step-up/step-down unit reactor 26c. Next, the negative side step-up/step-down unit second semiconductor switch 26d is turned off. At this time, as shown in FIG. 13, current flows from the negative side step-up/step-down unit reactor 26c → negative side step-up/step-down unit first diode 26b → power storage unit 6 → negative side step-up/step-down unit reactor 26c, and the power storage unit 6 is charged with the energy stored in the negative side step-up/step-down unit reactor 26c.

Next, the charging operation of the positive side capacitor 24a and the negative side capacitor 24b when an abnormality occurs in the AC power supply 1 will be described with reference to Figures 14 to 17. Figures 14 and 15 are first and second diagrams, respectively, used to explain the charging operation of the positive side capacitor 24a provided in the uninterruptible power supply 101 according to embodiment 2 when an abnormality occurs in the AC power supply 1. Figures 16 and 17 are first and second diagrams, respectively, used to explain the charging operation of the negative side capacitor 24b provided in the uninterruptible power supply 101 according to embodiment 2 when an abnormality occurs in the AC power supply 1.

First, when an abnormality occurs in the AC power supply 1, as shown in Figure 14, the contact of the AC power supply/battery selector switch 30 is switched to contact b, and the battery operation switch 31 is short-circuited. Then, when charging the positive side capacitor 24a, the converter section semiconductor switch 27b is controlled to be ON. At this time, as shown in Figure 14, current flows through the route of the power storage unit 6 → battery operation switch 31 → AC power supply/battery selector switch 30 → reactor 29 → diode 27a1 of the diode bridge 27a → converter section semiconductor switch 27b → diode 27a4 → power storage unit 6, and energy is stored in the reactor 29. Next, the converter section semiconductor switch 27b is controlled to be OFF. At this time, as shown in Figure 15, current flows through the reactor 29 → first reverse current prevention diode 21 → positive side capacitor 24a → power storage unit 6 → battery operation switch 31 → AC power supply/battery selector switch 30 → reactor 29, and the positive side capacitor 24a is charged by the energy stored in reactor 29.

When charging the negative capacitor 24b, the negative step-up/step-down unit first semiconductor switch 26a is turned on. At this time, as shown in FIG. 16, current flows from the power storage unit 6 to the negative step-up/step-down unit first semiconductor switch 26a to the negative step-up/step-down unit reactor 26c to the power storage unit 6, and energy is stored in the negative step-up/step-down unit reactor 26c. Next, the negative step-up/step-down unit first semiconductor switch 26a is turned off. At this time, as shown in FIG. 17, current flows from the negative step-up/step-down unit reactor 26c to the negative capacitor 24b to the negative step-up/step-down unit second diode 26e to the negative step-up/step-down unit reactor 26c, and the negative capacitor 24b is charged with the energy stored in the negative step-up/step-down unit reactor 26c.

When AC power is supplied to the load 4, an imbalance in the voltages of the positive-side capacitor 24a and the negative-side capacitor 24b may occur due to an imbalance in the load 4. Operation when such an imbalance occurs will be described with reference to Figures 18 to 21. Figures 18 and 19 are first and second diagrams, respectively, used to explain the operation for eliminating the imbalance when the voltage of the negative-side capacitor 24b, one of the positive-side capacitor 24a and the negative-side capacitor 24b provided in the uninterruptible power supply 101 according to embodiment 2, becomes high. Figures 20 and 21 are first and second diagrams, respectively, used to explain the operation for eliminating the imbalance when the voltage of the positive-side capacitor 24a, one of the positive-side capacitor 24a and the negative-side capacitor 24b provided in the uninterruptible power supply 101 according to embodiment 2, becomes high.

First, when the voltage of the negative side capacitor 24b becomes high, the balancing section second semiconductor switch 25c is controlled to be turned on. At this time, as shown in FIG. 18, current flows from the negative side capacitor 24b to the balancing section reactor 25e to the balancing section second semiconductor switch 25c to the negative side capacitor 24b, and energy is stored in the balancing section reactor 25e. Next, the balancing section second semiconductor switch 25c is controlled to be turned off. At this time, as shown in FIG. 19, current flows from the balancing section reactor 25e to the balancing section first diode 25b to the positive side capacitor 24a to the balancing section reactor 25e, and the positive side capacitor 24a is charged with the energy stored in the balancing section reactor 25e. This control transfers the charge in the negative side capacitor 24b to the positive side capacitor 24a, thereby eliminating the imbalance between the positive side capacitor 24a and the negative side capacitor 24b.

Furthermore, when the voltage of the positive side capacitor 24a becomes high, the balancing section first semiconductor switch 25a is controlled to be turned on. At this time, as shown in FIG. 20, current flows from the positive side capacitor 24a → balancing section first semiconductor switch 25a → balancing section reactor 25e → positive side capacitor 24a, and energy is stored in the balancing section reactor 25e. Next, the balancing section first semiconductor switch 25a is controlled to be turned off. At this time, as shown in FIG. 21, current flows from the balancing section reactor 25e → negative side capacitor 24b → balancing section second diode 25d → balancing section reactor 25e, and the negative side capacitor 24b is charged with the energy stored in the balancing section reactor 25e. This control transfers the charge of the positive side capacitor 24a to the negative side capacitor 24b, thereby eliminating the imbalance between the positive side capacitor 24a and the negative side capacitor 24b.

Also, as in embodiment 1, the control circuit 35 has a charging rate calculation unit that calculates the charging rate of the power storage unit 6 by a well-known method using the voltage of the power storage unit 6, etc. Also, as in embodiment 1, whether the load 4 performs regeneration is set by the setting unit 9. If the load 4 is a regenerative load, the charging rate will not be 100%, even if the AC power supply 1 is healthy. On the other hand, if the load 4 is a non-regenerative load, the charging rate will be 100%. Also, as in embodiment 1, the setting unit 9 may not be provided, and the upper limit of the charging rate of the power storage unit 6 may be determined based on the operating information output by the regeneration detection unit 12, i.e., information on whether the load 4 is performing regenerative operation or power running.

Next, we will explain the detailed operations of the balance unit 25, negative electrode step-up/step-down unit 26, and converter unit 27 when the AC power supply 1 is healthy. Note that the operations of these components when healthy also follow the flowchart in Figure 5, which was referenced in the explanation of embodiment 1. The following explanation will be made with reference to Figure 5.

First, in step S101, the charging rate calculation unit of the control circuit 35 calculates the charging rate of the power storage unit 6. In the next step S102, the regeneration detection unit 12 determines whether or not regenerative power from the load 4 is being detected. If regeneration is present (step S102, Yes), the process proceeds to step S104. If regeneration is not present (step S102, No), the process proceeds to step S103.

In step S103, it is determined whether the charging rate of the storage unit 6 calculated in step S101 is equal to or greater than a first threshold. The first threshold is set to, for example, 70%. If the charging rate of the storage unit 6 is equal to or greater than the first threshold (step S103, Yes), the process proceeds to step S105. If the charging rate is less than the first threshold (step S103, No), the process proceeds to step S106.

In step S105, discharge from the storage unit 6 to the negative capacitor 24b begins, and the processing flow in Figure 5 ends.

In step S105, there is no regeneration from the load 4 and the charge rate is equal to or greater than the first threshold. Therefore, in step S105, the power storage unit 6 is discharged to lower the charge rate of the power storage unit 6. This allows the power storage unit 6 to be charged with the regenerated power when there is regeneration from the load 4.

In step S106, it is determined whether the charging rate is less than a second threshold. The second threshold is a value smaller than the first threshold, and is set to, for example, 50%. If the charging rate is less than the second threshold (step S106, Yes), proceed to step S107. If the charging rate is equal to or greater than the second threshold (step S106, No), proceed to step S108.

Step S107 is a state in which there is no regeneration from the load 4 and the charging rate is less than the second threshold. That is, in step S107, the charging rate of the power storage unit 6 is sufficiently low, so charging of the power storage unit 6 begins and the processing flow in Figure 5 ends. Specifically, as shown in Figures 12 and 13, the negative side step-up/step-down unit 26 is operated to begin charging the power storage unit 6 and transfer charge from the negative side capacitor 24b to the power storage unit 6.

Step S108 is a state in which there is no regeneration from the load 4 and the charging rate is equal to or greater than the second threshold. In other words, step S108 is a state in which, if regeneration occurs, the regenerated power can be charged to the power storage unit 6, so charging and discharging of the power storage unit 6 is stopped and the processing flow in Figure 5 ends.

In step S104, it is determined whether the charging rate is less than 100%. If the charging rate is less than 100% (step S104, Yes), proceed to step S109; if the charging rate is 100% (step S104, No), proceed to step S110.

Step S109 is a state in which power is regenerated from the load 4 and the charging rate is less than 100%. That is, in step S109, the power storage unit 6 is not fully charged, so charging is performed from the negative side capacitor 24b to the power storage unit 6. Specifically, as shown in Figures 12 and 13, the negative side step-up/step-down unit 26 is operated to start charging the power storage unit 6 and transfer charge from the negative side capacitor 24b to the power storage unit 6. This allows the negative side capacitor 24b to accept regenerated power from the load 4, making effective use of the regenerated power.

Step S110 is a state in which regeneration is occurring from the load 4 and the charging rate is 100%. In other words, step S110 is a state in which the regenerative power from the load 4 cannot be further charged to the power storage unit 6, so charging is stopped.

The processing flow shown in Figure 5 is executed at preset intervals. The preset interval is set to, for example, 10 ms.

The uninterruptible power supply 101 according to the second embodiment also executes the processing flow shown in FIG. 5 while performing control according to the state of the AC power supply 1. Specifically, if the voltage of the AC power supply 1 drops below, for example, 90 V AC, which is the lower limit of the allowable voltage range, the uninterruptible power supply 101 determines that the AC power supply 1 has entered an abnormal state. In this case, the uninterruptible power supply 101 supplies power from the storage unit 6 to the positive-side capacitor 24a or the negative-side capacitor 24b via the negative-side step-up/step-down unit 26 or the converter unit 27, and controls the capacitor voltage to a predetermined value of 200 V DC. The uninterruptible power supply 101 also determines that the AC power supply 1 has entered an abnormal state if the voltage of the AC power supply 1 exceeds 110 V AC, which is the upper limit of the allowable voltage range, or if the capacitor voltage drops below, for example, 160 V, which is the lower limit of the predetermined value.

Furthermore, like the uninterruptible power supply 100 according to embodiment 1, the uninterruptible power supply 101 according to embodiment 2 performs backup operation, continuing to output an AC voltage of 100 V AC to the load 4 even when an abnormality occurs in the AC power supply 1. Backup operation continues until the voltage of the power storage unit 6 reaches a predetermined lower limit, for example, DC 50 V. If the voltage of the power storage unit 6 drops below DC 50 V, it is determined that the stored energy in the power storage unit 6 has been depleted, and power supply to the load 4 is stopped.

Next, we will explain the detailed operations of the balance unit 25, negative electrode step-up/step-down unit 26, and converter unit 27 during backup operation when the AC power supply 1 is abnormal. Note that the operations of these components during backup operation also follow the flowchart in Figure 6, which was referenced in the explanation of embodiment 1. The following explanation will be made with reference to Figure 6.

First, in step S201, the voltages of the positive-side capacitor 24a and the negative-side capacitor 24b are obtained from the capacitor voltage detection unit 8. In the next step S202, it is determined whether the voltage value obtained in step S201 is equal to or greater than a first value. The first value is a set value, and is set to DC 215 V, for example. If the voltage value is equal to or greater than the first value (step S202, Yes), the process proceeds to step S203. If the voltage value is less than the first value (step S202, No), the process proceeds to step S204.

In step S203, although backup operation is in progress, regeneration from the load 4 is occurring, and at least one of the voltages of the positive side capacitor 24a and the negative side capacitor 24b is equal to or greater than the first value. Therefore, to effectively utilize the regenerative power, charging of the power storage unit 6 begins. Specifically, as shown in Figures 12 and 13, the negative side step-up/step-down unit 26 is operated to begin charging the power storage unit 6 and transfer charge from the negative side capacitor 24b to the power storage unit 6. Alternatively, as shown in Figures 18 and 19, the balance unit 25 is operated to transfer charge from the negative side capacitor 24b to the positive side capacitor 24a. After processing step S203, the process proceeds to step S206.

In step S206, the charging rate of the power storage unit 6 is calculated, and the process proceeds to step S207.

In step S207, it is determined whether the charging rate is less than 100%. If the charging rate is less than 100% (step S207, Yes), the processing flow in Figure 6 ends. If the charging rate is 100% (step S207, No), the processing proceeds to step S208.

Step S208 indicates a state in which, during backup operation, charging of the power storage unit 6 begins when the capacitor voltage exceeds a first value due to regenerative power from the load 4, and charging then progresses until the charge rate of the power storage unit 6 reaches 100%. Therefore, further charging of the power storage unit 6 is no longer possible, so charging of the power storage unit 6 is stopped.

In step S204, it is determined whether the voltage value acquired in step S201 is less than a second value. The second value is a set value smaller than the first value, and is set to DC 200 V, for example. If the voltage value is less than the second value (step S204, Yes), the process proceeds to step S205. If the voltage value is equal to or greater than the second value (step S204, No), the process flow in Figure 6 ends.

Step S205 indicates that at least one of the voltages of the positive side capacitor 24a and the negative side capacitor 24b has dropped. Therefore, in step S205, charge is transferred to either the positive side capacitor 24a or the negative side capacitor 24b. Specifically, as shown in Figures 14 and 15, the converter unit 27 is operated to transfer charge from the storage unit 6 to the positive side capacitor 24a. Alternatively, as shown in Figures 16 and 17, the negative side step-up/step-down unit 26 is operated to transfer charge from the storage unit 6 to the negative side capacitor 24b.

The processing flow shown in Figure 6 is executed at preset intervals. The preset interval is set to, for example, 10 ms.

In the above description, the negative side step-up/step-down unit 26 or the converter unit 27 is operated without distinguishing between the voltages of the positive side capacitor 24a and the negative side capacitor 24b. However, the negative side step-up/step-down unit 26 or the converter unit 27 may be operated by distinguishing between the voltages of the positive side capacitor 24a and the negative side capacitor 24b. For example, when the voltage of the positive side capacitor 24a is less than the second value, as shown in FIGS. 14 and 15, the converter unit 27 may be operated to discharge the storage unit 6 and transfer charge from the storage unit 6 to the positive side capacitor 24a. Furthermore, when the voltage of the negative side capacitor 24b is less than the second value, as shown in FIGS. 16 and 17, the negative side step-up/step-down unit 26 may be operated to discharge the storage unit 6 and transfer charge from the storage unit 6 to the negative side capacitor 24b.

As described above, in the uninterruptible power supply according to embodiment 2, the third power conversion unit includes a negative-side step-up/step-down unit that transfers charge between the storage unit and the negative-side capacitor. When the AC power supply is abnormal and the voltage of the negative-side capacitor detected by the capacitor voltage detection unit is equal to or greater than a first value, the negative-side step-up/step-down unit operates to transfer the charge of the negative-side capacitor to the storage unit. This operation enables the capacitor to be in a state where it can accept regenerated power when regenerated from the load. This allows the regenerated power of the load to be used effectively.

The uninterruptible power supply according to embodiment 2 also includes a converter unit that operates as a first power conversion unit when the AC power supply is normal and that transfers charge from the storage unit to the positive-side capacitor when the AC power supply is abnormal. This converter unit operates to transfer charge from the storage unit to the positive-side capacitor when the AC power supply is abnormal and the voltage of the positive-side capacitor detected by the capacitor voltage detection unit is less than a second value that is smaller than the first value. Furthermore, the negative-side step-up/step-down unit operates to transfer charge from the storage unit to the negative-side capacitor when the AC power supply is abnormal and the voltage of the negative-side capacitor detected by the capacitor voltage detection unit is less than a second value that is smaller than the first value. This allows for uninterrupted power supply to the load even when the load switches from regenerative operation to power running.

The uninterruptible power supply according to embodiment 2 can also be configured to include a regeneration detection unit that detects the presence or absence of regenerative power from the load, and a charging rate calculation unit that calculates the charging rate of the power storage unit. In an uninterruptible power supply with this configuration, the negative-side step-up/step-down unit operates to transfer charge from the power storage unit to the negative-side capacitor when the AC power supply is healthy, the regeneration detection unit does not detect regenerative power, and the charging rate is equal to or greater than the first threshold. By transferring charge from the power storage unit to the capacitor, the charging rate of the power storage unit can be lowered. Furthermore, by lowering the charging rate of the power storage unit, when regeneration occurs from the load, the regenerative power of the load can be charged to the power storage unit. This allows the regenerative power of the load to be used effectively.

Furthermore, with the uninterruptible power supply according to embodiment 2, when the AC power supply is healthy, the regeneration detection unit detects regenerative power, and the charge rate is less than 100%, the negative-side step-up/step-down unit transfers charge from the negative-side capacitor to the power storage unit, and the fourth power conversion unit operates to transfer charge from the positive-side capacitor to the negative-side capacitor. This allows for a larger power capacity when accepting regenerative power from the load.

Finally, the hardware configuration for realizing the functions of the charge/discharge control unit 7d and control circuit 35 described above will be described with reference to Figures 22 and 23. Figure 22 is a block diagram showing an example of a hardware configuration for realizing the functions of the charge/discharge control unit 7d in embodiment 1 and the control circuit 35 in embodiment 2. Figure 23 is a block diagram showing another example of a hardware configuration for realizing the functions of the charge/discharge control unit 7d in embodiment 1 and the control circuit 35 in embodiment 2.

To realize some or all of the functions of the charge/discharge control unit 7d in embodiment 1 and the control circuit 35 in embodiment 2, the configuration can include a processor 300 that performs calculations, a memory 302 that stores programs read by the processor 300, and an interface 304 that inputs and outputs signals, as shown in FIG. 22.

Processor 300 is an example of a computing means. Processor 300 may be a computing means known as a microprocessor, microcomputer, CPU (Central Processing Unit), or DSP (Digital Signal Processor). Examples of memory 302 include non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), and EEPROM (registered trademark) (Electrically EPROM), as well as magnetic disks, flexible disks, optical disks, compact disks, minidisks, and DVDs (Digital Versatile Discs).

Memory 302 stores programs that execute the functions of charge/discharge control unit 7d in embodiment 1 and control circuit 35 in embodiment 2. Processor 300 exchanges necessary information via interface 304, executes the programs stored in memory 302, and references tables stored in memory 302, thereby performing the above-mentioned processing. The results of calculations performed by processor 300 can be stored in memory 302.

Furthermore, when implementing part of the functions of the charge/discharge control unit 7d in embodiment 1 and the control circuit 35 in embodiment 2, the processing circuit 303 shown in FIG. 23 can be used. The processing circuit 303 may be a single circuit, a composite circuit, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination of these. Information input to and output from the processing circuit 303 can be obtained via the interface 304.

In addition, some of the processing in the charge/discharge control unit 7d and control circuit 35 may be performed by the processing circuit 303, and other processing not performed by the processing circuit 303 may be performed by the processor 300 and memory 302.

The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies. Parts of the configuration may also be omitted or modified without departing from the spirit of the invention.

1 AC power supply, 2 First power conversion unit, 2a Bridge rectifier circuit, 2b Boost circuit, 3, 28, 33 Capacitor, 4 Load, 5 Second power conversion unit, 5a, 5b, 5c, 5d, 7b, 7c Self-extinguishing semiconductor switching element, 5e Filter circuit, 5f Single-phase full-bridge inverter, 6 Power storage unit, 7 Third power conversion unit, 7a, 29, 32 Reactor, 7d Charge/discharge control unit, 7e Voltage sensor, 8, 34 Capacitor voltage detection unit, 9 Setting unit, 10 Output voltage detection unit, 11 Current detection unit, 12 Regeneration detection unit, 21 First reverse current prevention diode, 22 Second reverse current prevention diode, 24 Inverter unit, 24a Positive side capacitor, 24b Negative side capacitor, 24c Inverter unit first semiconductor switch, 24d, 24f Inverter unit diode, 24e Inverter section second semiconductor switch, 25 balancing section, 25a balancing section first semiconductor switch, 25b balancing section first diode, 25c balancing section second semiconductor switch, 25d balancing section second diode, 25e balancing section reactor, 26 negative side step-up/step-down section, 26a negative side step-up/step-down section first semiconductor switch, 26b negative side step-up/step-down section first diode, 26c negative side step-up/step-down section reactor, 26d negative side step-up/step-down section second semiconductor switch, 26e negative side step-up/step-down section second diode, 27 converter section, 27a diode bridge, 27a1, 27a2, 27a3, 27a4 diode, 27b converter section semiconductor switch, 30 AC power supply/battery selector switch, 31 battery operation switch, 35 control circuit, 41 common line, 42 Positive voltage wire, 43 negative voltage wire, 44 connection point, 45 output wire, 100, 101 uninterruptible power supply, 300 processor, 302 memory, 303 processing circuit, 304 interface, a, b, c contacts.

Claims (8)

An uninterruptible power supply device including a power storage unit,
a first power conversion unit that converts power from an AC power supply into DC power;
a capacitor charged by the DC power;
a second power conversion unit that converts a DC output of the capacitor into AC power and outputs the AC power to a load;
a third power conversion unit that transfers charge from the capacitor to the power storage unit when the AC power supply is normal, and transfers charge from the power storage unit to the capacitor when the AC power supply is abnormal;
a voltage detection unit that detects a capacitor voltage, which is a voltage of the capacitor;
a regeneration detection unit that detects whether or not regenerative power is present from the load;
Equipped with
When the charge rate of the power storage unit is fully charged, it is 100%,
The third power conversion unit includes a charge/discharge control unit that controls charging/discharging of the power storage unit so as to maintain a charging rate of the power storage unit between a first threshold value that is smaller than 100% and a second threshold value that is smaller than the first threshold value when the AC power supply is healthy and the regeneration detection unit does not detect the regenerative power.
An uninterruptible power supply. The control for maintaining the charge rate of the power storage unit between the first threshold value and the second threshold value is executed at regular intervals.
2. The uninterruptible power supply according to claim 1. The third power conversion unit transfers the charge of the capacitor to the power storage unit when the capacitor voltage detected by the voltage detection unit is equal to or greater than a first value during an abnormality in the AC power supply.
2. The uninterruptible power supply according to claim 1. 4. The uninterruptible power supply device according to claim 3, wherein the third power conversion unit transfers charge from the storage unit to the capacitor when the capacitor voltage detected by the voltage detection unit becomes less than a second value that is smaller than the first value during an abnormality in the AC power supply. The capacitor comprises a positive-side capacitor and a negative-side capacitor,
5. The uninterruptible power supply according to claim 1, further comprising a fourth power conversion unit that transfers electric charges between the positive-side capacitor and the negative-side capacitor. The third power conversion unit
a negative-side step-up/step-down unit that moves charges between the power storage unit and the negative-side capacitor;
6. The uninterruptible power supply according to claim 5, further comprising a converter unit that also operates as the first power conversion unit when the AC power supply is normal, and that operates to transfer charge from the power storage unit to the positive-side capacitor when the AC power supply is abnormal. 7. The uninterruptible power supply according to claim 6, wherein when the AC power supply is abnormal and the voltage of the negative-side capacitor detected by the voltage detection unit is equal to or higher than a first value, the negative-side voltage step-up/step-down unit transfers the charge of the negative-side capacitor to the storage unit. When the AC power supply is abnormal and the voltage of the positive-side capacitor detected by the voltage detection unit is less than a second value that is smaller than the first value, the converter unit transfers charge from the power storage unit to the positive-side capacitor,
8. The uninterruptible power supply according to claim 7, wherein when the AC power supply is abnormal and the voltage of the negative side capacitor detected by the voltage detection unit is less than a second value that is smaller than the first value, the negative side voltage step-up/step-down unit transfers charge from the storage unit to the negative side capacitor.