Single energy storage device for voltage balancing of bipolar DC microgrid and voltage balancing method using same

Abstract

The present invention relates to a single energy storage device for voltage balancing of a bipolar DC microgrid and a voltage balancing method using same, and more particularly, to a single energy storage device for voltage balancing of a bipolar DC microgrid and a voltage balancing method using same, wherein voltage imbalance between a positive electrode and a negative electrode can be resolved while storing and supplying power through the single energy storage device installed in the bipolar DC microgrid.

Description

Single energy storage device for voltage balancing of a bipolar DC microgrid and voltage balancing method using the same

[0001] The present invention relates to a single energy storage device for voltage balancing of a bipolar DC microgrid and a voltage balancing method using the same, and more specifically, to a single energy storage device for voltage balancing of a bipolar DC microgrid and a voltage balancing method using the same, which can store and supply power through a single energy storage device installed in a bipolar DC microgrid while simultaneously resolving voltage imbalance between a positive electrode and a negative electrode.

[0002] Recently, DC microgrids have been attracting attention due to advancements in power and electronic technologies and the growth of distributed energy resources such as solar, wind, and electric transport. Since DC microgrids do not generate reactive power, there are no transmission losses caused by reactive current, and they are efficient as they can eliminate the AC / DC conversion stage.

[0003] Generally, DC microgrid configurations are classified into unipolar and bipolar DC microgrids. Unipolar DC microgrids transmit power through two wires at a single voltage level, enabling high-power transmission using high voltage. However, there are drawbacks: using high voltage levels requires an additional converter, while using low voltage levels limits long-distance energy transfer.

[0004] A bipolar DC microgrid includes three transmission lines: a positive pole, a negative pole, and a neutral pole. This structure allows for two voltage levels depending on whether the reference potential point is set to neutral or negative. In the case of such a bipolar DC microgrid, power can be supplied through the other DC pole and an auxiliary converter even if a fault occurs in one of the DC poles, thereby providing higher reliability and safety compared to a unipolar DC microgrid.

[0005] However, even with these bipolar DC microgrids, voltage imbalance issues arise if the load is uneven between the poles. While a voltage balancer can be configured near the rectifier to resolve this problem, installing multiple voltage balancers incurs significant costs.

[0006] The present invention was created to solve such problems, and the objective of the present invention is to provide a single energy storage device for voltage balancing of a bipolar DC microgrid and a voltage balancing method using the same, which can store and supply power through a single energy storage device installed in a bipolar DC microgrid while simultaneously resolving voltage imbalance between the positive and negative electrodes.

[0007] A single energy storage device for voltage balancing of a bipolar DC microgrid according to the present invention, for achieving the above-mentioned purpose, is characterized by comprising: a master converter control unit that performs battery charging or discharging control according to a charging or discharging signal (Ems); and a slave converter control unit that performs control to resolve voltage imbalance when it occurs according to the battery charging or discharging control of the master converter control unit.

[0008] In addition, the master converter control unit is characterized by including a first inductor for performing battery charging or discharging control; a first switch; and a second switch.

[0009] In addition, the master converter control unit is characterized by controlling the first inductor to turn off the first switch and turn on the second switch in order to perform battery charging control.

[0010] In addition, the master converter control unit is characterized by controlling a first inductor to turn on a first switch and turn off a second switch in order to perform battery discharge control.

[0011] In addition, the slave converter control unit is characterized by including a second inductor for performing voltage imbalance resolution control; a third switch; and a fourth switch.

[0012] In addition, the slave converter control unit is characterized by comparing the Vpo voltage and the Vno voltage when a voltage imbalance occurs, and if the Vpo voltage is higher than the Vno voltage, controlling the second inductor to turn on the third switch and turn off the fourth switch to boost the Vno voltage.

[0013] In addition, the slave converter control unit is characterized by comparing the Vpo voltage and the Vno voltage when a voltage imbalance occurs, and if the Vpo voltage is lower than the Vno voltage, controlling the second inductor to turn off the third switch and turn on the fourth switch to reduce the Vno voltage.

[0014] A voltage balancing method for a bipolar DC microgrid using a single energy storage device according to the present invention for achieving the above-mentioned purpose is characterized by comprising: step A, in which a master converter control unit performs battery charging or discharging control according to a charging or discharging signal (Ems); and step B, in which a slave converter control unit performs control to resolve voltage imbalance when it occurs according to the battery charging or discharging control of the master converter control unit.

[0015] In addition, the master converter control unit is characterized by including a first inductor for performing battery charging or discharging control; a first switch; and a second switch.

[0016] In addition, the master converter control unit is characterized by controlling the first inductor to turn off the first switch and turn on the second switch in order to perform battery charging control.

[0017] In addition, the master converter control unit is characterized by controlling a first inductor to turn on a first switch and turn off a second switch in order to perform battery discharge control.

[0018] In addition, the slave converter control unit is characterized by including a second inductor for performing voltage imbalance resolution control; a third switch; and a fourth switch.

[0019] In addition, the slave converter control unit is characterized by comparing the Vpo voltage and the Vno voltage when a voltage imbalance occurs, and if the Vpo voltage is higher than the Vno voltage, controlling the second inductor to turn on the third switch and turn off the fourth switch to boost the Vno voltage.

[0020] In addition, the slave converter control unit is characterized by comparing the Vpo voltage and the Vno voltage when a voltage imbalance occurs, and if the Vpo voltage is lower than the Vno voltage, controlling the second inductor to turn off the third switch and turn on the fourth switch to reduce the Vno voltage.

[0021] The single energy storage device and voltage balancing method for voltage balancing of a bipolar DC microgrid according to the present invention have the effect of storing and supplying power through a single energy storage device installed in a bipolar DC microgrid while simultaneously resolving voltage imbalance between the positive and negative electrodes.

[0022] In addition, by installing a single energy storage device that integrates the functions of a bidirectional converter and a voltage balancer, the voltage imbalance problem of a bipolar DC microgrid can be resolved, eliminating the need to build a separate additional energy storage device and voltage balancer and minimizing installation costs.

[0023] The problems solved by the present invention are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0024] Figure 1 is an example configuration diagram of a voltage balancer installed in a typical bipolar DC microgrid.

[0025] FIG. 2 is a circuit diagram of a single energy storage device for voltage balancing of a bipolar DC microgrid according to an embodiment of the present invention.

[0026] FIG. 3 is a circuit diagram of a master converter control unit according to an embodiment of the present invention.

[0027] FIG. 4 is a circuit diagram of a slave converter control unit according to an embodiment of the present invention.

[0028] FIG. 5 is a flowchart of a voltage balancing method for a bipolar DC microgrid using a single energy storage device according to an embodiment of the present invention.

[0029] FIG. 6 is an example diagram of the operation of a slave control unit during discharge control of a master converter control unit according to an embodiment of the present invention.

[0030] FIG. 7 is an example of the operation of a slave control unit during discharge control of a master converter control unit according to an embodiment of the present invention.

[0031] FIG. 8 is an example diagram of the operation of a slave control unit during charging control of a master converter control unit according to an embodiment of the present invention.

[0032] FIG. 9 is an example of the operation of a slave control unit during charging control of a master converter control unit according to an embodiment of the present invention.

[0033] FIG. 10 is an example diagram of the operation waveforms of components according to an embodiment of the present invention.

[0034] The above objects, other objects, features, and advantages of the present invention will be easily understood through the following preferred embodiments associated with the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed content is thorough and complete, and to ensure that the spirit of the present invention is sufficiently conveyed to those skilled in the art.

[0035] Where in this specification it is stated that any element, component, device, or system comprises a component consisting of a program or software, it should be understood that, even without explicit mention, the element, component, device, or system comprises hardware (e.g., memory, CPU, etc.) or other programs or software (e.g., an operating system or drivers required to run the hardware) necessary for the program or software to execute or operate.

[0036] Furthermore, unless otherwise specified regarding the implementation of any element (or component), it should be understood that the element (or component) may be implemented in software, hardware, or in any form that combines both software and hardware.

[0037] Furthermore, the terms used herein are for the purpose of describing embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used in this specification, 'comprises' and / or 'comprising' do not exclude the presence or addition of one or more other components to the mentioned components.

[0038] Additionally, in this specification, terms such as 'part', 'device', etc., may be intended to refer to hardware and the functional and structural combination of software driven by said hardware or for driving said hardware. For example, the hardware here may be a data processing device including a CPU or other processor. Furthermore, the software driven by the hardware may refer to a running process, object, executable, thread of execution, program, etc.

[0039]

[0040] Hereinafter, specific technical details to be implemented in the present invention will be described in detail with reference to the attached drawings.

[0041] An average person skilled in the art will readily infer that each component depicted in the drawings indicates that it can be functionally and logically separated, and does not necessarily mean that each component is distinguished as a separate physical device or written in separate code.

[0042]

[0043] First, FIG. 1 is an example diagram of the configuration of a voltage balancer installed in a typical bipolar DC microgrid. As shown in FIG. 1, a voltage balancer for a typical bipolar DC microgrid is composed of switches (S1, S2), loads (R1, R2), inductors (L1), capacitors (C1, C2), etc. Here, if R1 is greater than R2, it means that the load power of the positive electrode is smaller than the load power of the negative electrode, and conversely, if R2 is greater than R1, it indicates that the load power of the negative electrode is smaller than the load power of the positive electrode.

[0044] When R1 connected to the positive electrode increases, a PWM signal is applied to switch S1 to supply unbalanced power to the negative electrode, and when R2 connected to the negative electrode increases, switch S2 operates to supply unbalanced power to the positive electrode. The above voltage balancer reduces the voltage imbalance between the positive and negative electrodes through such switching control, but as previously explained, there are cost-related issues when installing multiple voltage balancers.

[0045]

[0046] FIG. 2 is a circuit diagram of a single energy storage device for voltage balancing of a bipolar DC microgrid according to an embodiment of the present invention. As shown in FIG. 2, the single energy storage device for voltage balancing of a bipolar DC microgrid according to the present invention may include a master converter control unit (100) and a slave converter control unit (200).

[0047] In addition to the above configuration, it may further include two or more capacitors (C1, C2), two or more loads (R1, R2), and a power supply (Vi).

[0048] The above master converter control unit (100) is configured to perform battery charging or discharging of an energy storage device according to a charging or discharging signal (Ems), and may include a first inductor (110), a first switch (120), and a second switch (130). As shown in FIG. 3, the first inductor (110) can be controlled to turn the first switch (120) and the second switch (130) on / off according to the charging or discharging signal (Ems). FIG. 3 is a circuit diagram of a master converter control unit according to an embodiment of the present invention.

[0049] The slave converter control unit (200) is configured to perform control to resolve voltage imbalance when the master converter control unit (100) performs battery charging or discharging control. It may include a second inductor (210), a third switch (220), and a fourth switch (230). As shown in FIG. 4, the second inductor (210) can be controlled to turn the third switch (220) and the fourth switch (230) on / off according to a balancing signal (Ebal) and a slave signal (Esl). FIG. 4 is a circuit diagram of a slave converter control unit according to an embodiment of the present invention.

[0050]

[0051] Hereinafter, a voltage balancing method for a bipolar DC microgrid using a single energy storage device according to the present invention configured as described above will be explained in detail through FIGS. 5 to 10.

[0052]

[0053] FIG. 5 is a flowchart of a voltage balancing method for a bipolar DC microgrid using a single energy storage device according to an embodiment of the present invention. As shown in FIG. 5, the voltage balancing method for a bipolar DC microgrid using a single energy storage device according to the present invention first includes a step (S100) in which a master converter control unit (100) receives a charge or discharge signal (Ems).

[0054] In the above step (S100), if the charging or discharging signal (Ems) is 1, it means a charging signal, and the master converter control unit (100) controls the first inductor (110) to turn off the first switch (120) and turn on the second switch (130) in order to perform battery charging control.

[0055] Conversely, when the above charging or discharging signal (Ems) is 0, it means a discharge signal, and the master converter control unit (100) controls the first inductor (110) to turn on the first switch (120) and turn off the second switch (130) in order to perform battery discharge control.

[0056] The control of the above-described master converter control unit (100) is performed by dual-loop control, where the inner control loop controls the inductor current and the outer control loop controls the capacitor voltage.

[0057]

[0058] Next, the voltage balancing method of a bipolar DC microgrid using a single energy storage device according to the present invention includes a step (S200) in which a slave converter control unit (200) compares a positive voltage (Vpo voltage) and a negative voltage (Vno voltage).

[0059] In the above step (S200), if the Vpo voltage and Vno voltage are the same, it is not because a voltage imbalance has occurred, so the balancing signal (Ebal) 0 is input, and the slave converter control unit (200) does not operate the third switch (220) and the fourth switch (230).

[0060] However, if the above Vpo voltage and Vno voltage are not the same, a voltage imbalance has occurred, so a balancing signal (Ebal) 1 is input, and the slave converter control unit (200) performs the operation of the third switch (220) and the fourth switch (230) to resolve the voltage imbalance.

[0061] At this time, the slave converter control unit (200) compares the Vpo voltage and the Vno voltage, and if the Vpo voltage is higher than the Vno voltage, controls the second inductor (210) to turn on the third switch (220) and turn off the fourth switch (230) to increase the Vno voltage and resolve the voltage imbalance.

[0062] Conversely, the slave converter control unit (200) compares the Vpo voltage and the Vno voltage, and if the Vpo voltage is lower than the Vno voltage, controls the second inductor (210) to turn off the third switch (220) and turn on the fourth switch (230) to reduce the Vno voltage and resolve the voltage imbalance.

[0063] The control of the above-described slave converter control unit (200) is performed by dual-loop control, similar to the master converter control unit (100), where the inner control loop controls the inductor current and the outer control loop controls the capacitor voltage.

[0064] The above-mentioned steps (S100~S200) are explained in more detail as shown in FIGS. 6 to 9.

[0065] First, FIG. 6 is an example of the operation of a slave converter control unit during discharge control of a master converter control unit according to an embodiment of the present invention. As shown in FIG. 6, when a single energy storage device according to the present invention performs battery discharge control and a voltage imbalance occurs such that the Vpo voltage is higher than the Vno voltage, the control of the single energy storage device to resolve this can be described in three steps. First, in the first step (S1), the first switch (120) and the third switch (220) are turned on simultaneously, and inductor currents iL1 and iL2 flow through the first switch (120) and the third switch (220). At this time, the inductor voltages VL1 and VL2 are equal to Equation 1 below, the capacitor current ic1 is equal to Equation 2 below, and ic2 is equal to Equation 3 below, and the slope of ii in the first step (S1) is equal to Equation 4 below.

[0066]

[0067]

[0068]

[0069]

[0070] Next, in the second step (S2), the first switch (120) is turned on and the third switch (220) is turned off. At this time, VL1 and ic1 are as in Equations 1 and 2 above, but VL2 is as in Equation 5 below and ic2 is as in Equation 6 below, and the slope of ii in the second step (S2) is as in Equation 7 below. Then, the energy accumulated in L2 is transferred to Vno through the body diode of the fourth switch (230).

[0071]

[0072]

[0073]

[0074] Finally, in the third step (S3), the first switch (120) and the third switch (220) are turned off. iL1 flows to Vpn through the body diode of the second switch (130), and the inductor voltage VL1 is given by Equation 8 below, and VL2 is given by Equation 5 above. The capacitor current ic1 is given by Equation 9 below, and ic2 is given by Equation 10 below, and the slope of ii in the third step (S3) is given by Equation 11 below.

[0075]

[0076]

[0077]

[0078]

[0079] In the above steps (S1~S3), the average inductor voltage (VL1.avg, VL2.avg) is given by Equations 12 and 13 below, and the voltage transfer ratio (Gv1, Gv3) is given by Equations 14 and 15 below. In addition, the relationship between d1 and d3 is given by Equation 16.

[0080]

[0081]

[0082]

[0083]

[0084]

[0085] That is, through the above-described steps (S1~S3), the single energy storage device according to the present invention can simultaneously perform battery discharge control and voltage imbalance resolution control.

[0086]

[0087] FIG. 7 is an example of the operation of a slave converter control unit during discharge control of a master converter control unit according to an embodiment of the present invention. As shown in FIG. 7, when a single energy storage device according to the present invention performs battery discharge control and a voltage imbalance occurs such that the Vpo voltage is lower than the Vno voltage, the control of the single energy storage device to resolve this can be described in three steps. First, in the first step (S4), the first switch (120) and the fourth switch (230) are turned on simultaneously, and inductor currents iL1 and iL2 flow through the first switch (120) and the fourth switch (230). At this time, the inductor voltage VL1 is equal to Equation 1 above, VL2 is equal to Equation 17 below, the capacitor current ic1 is equal to Equation 2 above, and ic2 is equal to Equation 10 above. The slope of ii in the above first step (S4) is equal to the following mathematical formula 18.

[0088]

[0089]

[0090] Next, in the second step (S5), the first switch (120) is turned off, and the fourth switch (230) is turned on. The energy accumulated in L1 is transferred to Vpm through the body diode of the second switch (130). At this time, the inductor voltage VL1 is equal to Equation 8 above, and VL2 is equal to Equation 17 above. The inductor current iL1 is equal to Equation 9 above, and the capacitor current ic2 is equal to Equation 7 above. In the second step (S5), the slope of ii is equal to Equation 19 below.

[0091]

[0092] Finally, in the third step (S6), the first switch (120) and the fourth switch (230) are turned off. The inductor current iL2 flows to L1 through the body diode of the third switch (220), the inductor voltage VL1 is equal to Equation 10 above, and VL2 is equal to Equation 20 below. The unbalanced current iun is equal to Equation 3 above, and the slope of ii in the third step (S6) is equal to Equation 21 below.

[0093]

[0094]

[0095] In the steps (S4~S6) described above, the average inductor voltage VL1.avg is given by Equation 12 above, and VL2.avg is given by Equation 22 below. The voltage transfer ratio Gv1 is given by Equation 14 above, and Gv4 is given by Equation 23 below. In addition, the relationship between d1 and d4 is given by Equation 24 below.

[0096]

[0097]

[0098]

[0099] That is, through the steps (S4~S6) described above, the single energy storage device according to the present invention can simultaneously perform battery discharge control and voltage imbalance resolution control.

[0100]

[0101] FIG. 8 is an example of the operation of a slave converter control unit during charging control by a master converter control unit according to an embodiment of the present invention. As shown in FIG. 8, when a single energy storage device according to the present invention performs battery charging control and a voltage imbalance occurs such that the Vpo voltage is higher than the Vno voltage, the control of the single energy storage device to resolve this can be described in three steps. First, in the first step (S7), the second switch (130) and the third switch (220) are turned on simultaneously, the inductor current iL1 flows toward the Vi side and is divided into iL2 and ii, and the capacitor currents ic1 and ic2 flow toward the iun side as shown in Equation 26 below. At this time, the inductor voltage VL1 is as shown in Equation 25 below, VL2 is as shown in Equation 1 above, and in the first step (S7), ii is as shown in Equation 27 below.

[0102]

[0103]

[0104]

[0105] Next, in the second step (S8), the second switch (130) is turned on and the third switch (220) is turned off, and iL2 flows to the Vno side through the body diode of the fourth switch (230). At this time, VL1 is equal to Equation 25 above, and VL2 is equal to Equation 5 above. The inductor current iL2 is equal to Equation 28 below, and the slope of ii in the second step (S8) is equal to Equation 29 below.

[0106]

[0107]

[0108] Finally, in the third step (S9), the second switch (130) and the third switch (220) are turned off, and the energy accumulated in L1 is transferred to the Vi side through the body diode of the first switch (120). At this time, the inductor voltage VL1 is equal to Equation 30 below, and VL2 is equal to Equation 5 above. The inductor current iL2 is equal to Equation 31 below, and ic1 is equal to Equation 2 above. In the third step (S9), the slope of ii is equal to Equation 32 below.

[0109]

[0110]

[0111]

[0112] In the steps (S7~S9) above, the average inductor voltage VL1.avg is given by Equation 33 below, and VL2.avg is given by Equation 13 above. The voltage transfer ratio Gv2 is given by Equation 34 below. In addition, the relationship between d2 and d3 is given by Equation 35 below.

[0113]

[0114]

[0115]

[0116] That is, through the steps (S7~S9) described above, the single energy storage device according to the present invention can simultaneously perform battery charging control and voltage imbalance resolution control.

[0117]

[0118] FIG. 9 is an example of the operation of a slave converter control unit during charging control by a master converter control unit according to an embodiment of the present invention. As shown in FIG. 7, when a single energy storage device according to the present invention performs battery charging control and a voltage imbalance occurs such that the Vpo voltage is lower than the Vno voltage, the control of the single energy storage device to resolve this can be described in three steps. First, in the first step (S10), the second switch (130) and the fourth switch (230) are turned on simultaneously. At this time, the inductor voltage VL1 is equal to Equation 25 above, VL2 is equal to Equation 17 above, and the unbalanced current iun is equal to Equation 36 below. Since iL1 and iL2 flow toward the Vi side, ii increases linearly in the first step (S10) and is equal to Equation 37 below.

[0119]

[0120]

[0121]

[0122] Next, in the second step (S11), the second switch (120) is turned off and the fourth switch (230) is turned on, and the inductor current iL1 flows to the Vi side through the body diode of the first switch (120). At this time, VL1 is equal to Equation 30 above, VL2 is equal to Equation 17 above, the capacitor current ic1 flows to the positive load, and the unbalanced current iun is equal to Equation 38 below. In the second step (S11), the slope of ii is equal to Equation 39 below.

[0123]

[0124]

[0125] Finally, in the third step (S12), the second switch (130) and the fourth switch (230) are turned off, and the energy remaining in each inductor is transferred to the Vi side through the body diodes of the second switch (130) and the fourth switch (230). At this time, the inductor voltages VL1 and VL2 are equal to Equation 1 above, and the unbalanced current iun is equal to Equation 40 below. In the third step (S12), the slope of ii is equal to Equation 41 below.

[0126]

[0127]

[0128] In the steps (S9~S12) described above, the average inductor voltage VL1.avg is equal to Equation 33 above, and VL2.avg is equal to Equation 22 above. Also, the relationship between d2 and d4 is equal to Equation 42 below.

[0129]

[0130] That is, through the steps (S9~S12) described above, the single energy storage device according to the present invention can simultaneously perform battery charging control and voltage imbalance resolution control.

[0131]

[0132] FIG. 10 is an example diagram of the operation waveforms of components according to an embodiment of the present invention. As shown in FIG. 10, it can be confirmed through the operation waveforms that a single energy storage device according to the present invention can perform battery charging or discharging control and, at the same time, simultaneously perform voltage imbalance resolution control when a voltage imbalance occurs.

[0133]

[0134] In the foregoing, although all components constituting an embodiment of the present invention have been described as being combined or operating as a single unit, the present invention is not necessarily limited to such an embodiment. That is, within the scope of the purpose of the present invention, all components may be selectively combined and operated in one or more ways. Furthermore, while all components may each be implemented as a single independent piece of hardware, some or all of the components may be selectively combined to be implemented as a computer program having a program module that performs some or all of the combined functions on one or more pieces of hardware. The codes and code segments constituting the computer program can be easily inferred by those skilled in the art of the present invention. An embodiment of the present invention may be implemented by storing such a computer-readable storage medium and reading and executing it by a computer.

[0135]

[0136] Meanwhile, although preferred embodiments illustrating the technical concept of the present invention have been described and illustrated above, the present invention is not limited to the configuration and operation as illustrated and described, and those skilled in the art will understand that numerous changes and modifications are possible to the present invention without departing from the scope of the technical concept. Accordingly, all such appropriate changes, modifications, and equivalents should be deemed to fall within the scope of the present invention. Accordingly, the true scope of technical protection of the present invention should be determined by the technical concept of the appended claims.

[0137] The present invention can be used in a single energy storage device for voltage balancing of a bipolar DC microgrid, etc.

Claims

1. A master converter control unit that performs battery charging or discharging control according to a charging or discharging signal (Ems); and A single energy storage device for voltage balancing of a bipolar DC microgrid, characterized by including: a slave converter control unit that performs control to resolve voltage imbalance when it occurs according to the battery charging or discharging control of the master converter control unit.

2. In Paragraph 1, The above master converter control unit is, A first inductor for performing battery charging or discharging control; First switch; and Second switch; A single energy storage device for voltage balancing of a bipolar DC microgrid characterized by including 3. In Paragraph 2, The above master converter control unit is, A single energy storage device for voltage balancing of a bipolar DC microgrid, characterized by controlling a first inductor to turn off a first switch and turn on a second switch in order to perform battery charging control.

4. In Paragraph 2, The above master converter control unit is, A single energy storage device for voltage balancing of a bipolar DC microgrid, characterized by controlling a first inductor to turn on a first switch and turn off a second switch in order to perform battery discharge control.

5. In Paragraph 1, The above slave converter control unit is, A second inductor for performing voltage imbalance resolution control; Third switch; and Fourth switch; A single energy storage device for voltage balancing of a bipolar DC microgrid, characterized by including 6. In Paragraph 5, The above slave converter control unit is, A single energy storage device for voltage balancing of a bipolar DC microgrid, characterized by comparing Vpo voltage and Vno voltage when a voltage imbalance occurs, and if Vpo voltage is higher than Vno voltage, controlling a second inductor to turn on a third switch and turn off a fourth switch to boost Vno voltage.

7. In Paragraph 5, The above slave converter control unit is, A single energy storage device for voltage balancing of a bipolar DC microgrid, characterized by comparing Vpo voltage and Vno voltage when a voltage imbalance occurs, and if Vpo voltage is lower than Vno voltage, controlling a second inductor to turn off a third switch and turn on a fourth switch to reduce Vno voltage.

8. Step A in which the master converter control unit performs battery charging or discharging control according to a charging or discharging signal (Ems); and A voltage balancing method for a bipolar DC microgrid using a single energy storage device, characterized by including: Step B, in which a slave converter control unit performs control to resolve a voltage imbalance when it occurs according to the battery charging or discharging control of the master converter control unit.

9. In Paragraph 8, The above master converter control unit is, A first inductor for performing battery charging or discharging control; First switch; and Second switch; A voltage balancing method for a bipolar DC microgrid using a single energy storage device, characterized by including 10. In Paragraph 9, The above master converter control unit is, A voltage balancing method for a bipolar DC microgrid using a single energy storage device, characterized by controlling a first inductor to turn off a first switch and turn on a second switch in order to perform battery charging control.

11. In Paragraph 9, The above master converter control unit is, A voltage balancing method for a bipolar DC microgrid using a single energy storage device, characterized by controlling a first inductor to turn on a first switch and turn off a second switch in order to perform battery discharge control.

12. In Paragraph 8, The above slave converter control unit is, A second inductor for performing voltage imbalance resolution control; Third switch; and Fourth switch; A voltage balancing method for a bipolar DC microgrid using a single energy storage device, characterized by including 13. In Paragraph 12, The above slave converter control unit is, A voltage balancing method for a bipolar DC microgrid using a single energy storage device, characterized by comparing Vpo voltage and Vno voltage when a voltage imbalance occurs, and if Vpo voltage is higher than Vno voltage, controlling a second inductor to turn on a third switch and turn off a fourth switch to boost Vno voltage.

14. In Paragraph 12, The above slave converter control unit is, A voltage balancing method for a bipolar DC microgrid using a single energy storage device, characterized by comparing Vpo voltage and Vno voltage when a voltage imbalance occurs, and if Vpo voltage is lower than Vno voltage, controlling a second inductor to turn off a third switch and turn on a fourth switch to reduce Vno voltage.

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