KR20200017947A - A votage balancer with dc-dc converter function - Google Patents

Abstract

Disclosed is a voltage balancer with a direct current (DC)-DC converter function. The voltage balancer with the DC-DC converter function comprises: a bipolar DC bus unit including lines connected to a positive terminal, a negative terminal and a neutral terminal, respectively; a DC-DC converter unit connected in parallel with each line of the bipolar DC bus unit, including a plurality of switches and supplying power to a load; and a control unit controlling the plurality of switches of the DC-DC converter unit to balance a magnitude of a first voltage between the positive terminal and the negative terminal and a magnitude of a second voltage between the negative terminal and the neutral terminal so as to supply the power to the load at the same time.

Description

Voltage balancer with DC-DC converter function {A VOTAGE BALANCER WITH DC-DC CONVERTER FUNCTION}

The present disclosure relates to a voltage balancer, and more particularly, to a voltage balancer including a DC-DC converter function.

Recently, due to the increase in distributed power sources and DC-based digital loads using renewable energy, research on DC distribution has been actively conducted. The DC power distribution method can increase power efficiency and power density compared to the AC power distribution method, does not generate reactive power and does not require system synchronization. DC distribution networks are divided into unipolar distribution networks and bipolar distribution networks depending on the number of possible voltage levels. Bipolar power distribution network is easier to connect with loads and distribution networks having various ratings than unipolar power distribution network, and can increase system reliability and stability because neutral wire is connected to ground.

However, the bipolar power distribution network has a disadvantage in that voltage unbalance occurs when the load power consumption of each pole is different. Voltage unbalance can degrade voltage quality, cause failures in precise loads, and damage switching devices. Therefore, the bipolar power distribution network always needs an additional voltage balancer to solve the voltage unbalance.

Recently, a method for solving voltage unbalance based on a three-level (DC) DC-DC converter in a fast charger for an electric vehicle has been proposed. 1 shows an overall system including a three-level DC-DC converter. The TL converter can act as a quick charger while maintaining voltage balance across each pole. The proposed system can increase the voltage compensation range compared to the conventional system that performs voltage balance control by NPC alone through the voltage balance control of Neutral-Point-Clamped (NPC) and TL converters, and requires an additional voltage balancer circuit. There is no advantage.

However, the voltage compensation range of the system is limited by the output power of the TL converter, and as a result, there is a disadvantage in that an unbalanced voltage cannot be compensated if all the rapid chargers are not operating.

Therefore, there is a need for a system that can compensate for an unbalanced voltage even without power transfer between a bipolar power distribution network and an ESS (Energy Storage System), and does not limit the voltage compensation range.

The present disclosure is to solve the above-described problems, an object of the present disclosure is to provide a voltage balancer that includes a DC-DC converter function that can solve the voltage unbalance without charging the voltage compensation range and at the same time.

According to an exemplary embodiment of the present disclosure for achieving the above object, a voltage balancer including a DC-DC converter function includes a bipolar DC bus unit including a line connected to a positive terminal, a negative terminal, and a neutral terminal, respectively, the bipolar A DC-DC converter unit connected in parallel with each line of the DC bus unit and including a plurality of switches and supplying power to a load, and a magnitude of a first voltage between the positive terminal and the neutral terminal and between the negative terminal and the neutral terminal And a control unit controlling a plurality of switches of the DC-DC converter unit to balance power of the second voltage and simultaneously supply power to the load.

The DC-DC converter unit includes a first capacitor connected between the positive terminal and the neutral terminal and a second capacitor connected between the negative terminal and the neutral terminal, and the bipolar DC bus unit is parallel to the first capacitor. It may include a first resistor connected to and a second resistor connected in parallel with the second capacitor.

The DC-DC converter may include a first switch disposed in series with a line connected to the negative terminal, a second switch disposed in series with a line connected with the positive terminal, and a line connected with the neutral terminal and the first switch. It may include a third switch connected to one end and a fourth switch connected to one end of the first switch and one end of the second switch.

The controller may include a voltage balance function that complementarily turns on and off the first switch and the third switch, and alternately turns on and off the second switch and the fourth switch. .

The controller may sequentially turn on and off the first switch and the second switch based on a preset ratio.

When the first voltage is greater than the second voltage, the controller reduces a preset ratio of turning on the first switch to balance the magnitude of the first voltage and the magnitude of the second voltage. When the second voltage is greater than the first voltage, a preset ratio of turning on the first switch may be increased to balance the magnitude of the first voltage and the magnitude of the second voltage.

As described above, according to various embodiments of the present disclosure, the voltage balancer including the DC-DC converter function may solve the voltage unbalance at the same time as charging without limiting the voltage compensation range.

1 is a diagram illustrating a system including a conventional TL DC-DC converter.
2 is a block diagram of a voltage balancer including a DC-DC converter function according to an embodiment of the present disclosure.
3 is a circuit diagram of a voltage balancer including a DC-DC converter function according to an embodiment of the present disclosure.
4 is a diagram illustrating an operation mode of a voltage balancer including a DC-DC converter function in a state in which a load is not connected according to an embodiment of the present disclosure.
FIG. 5 is a diagram illustrating waveforms according to an operation mode of a voltage balancer including a DC-DC converter function when no load is connected.
FIG. 6 is a diagram illustrating waveforms according to an operation mode of a voltage balancer including a DC-DC converter function when a load is connected.
7 is a diagram illustrating a control process of a controller according to one embodiment of the present disclosure.
8 is a diagram illustrating a simulation result of a voltage balancer including a DC-DC converter function when no load is connected.
9 is a diagram illustrating a simulation result of a voltage balancer including a DC-DC converter function when a load is connected.
FIG. 10 illustrates an experimental result of a voltage balancer including a DC-DC converter function according to an embodiment of the present disclosure.

Hereinafter, various embodiments will be described in more detail with reference to the accompanying drawings. Embodiments described herein may be variously modified. Specific embodiments may be depicted in the drawings and described in detail in the detailed description. However, the specific embodiments disclosed in the accompanying drawings are only for easily understanding the various embodiments. Therefore, the technical spirit is not limited by the specific embodiments disclosed in the accompanying drawings, and it should be understood to include all equivalents or substitutes included in the spirit and scope of the invention.

 Terms including ordinal numbers such as first and second may be used to describe various components, but these components are not limited by the terms described above. The terms described above are used only for the purpose of distinguishing one component from another.

As used herein, the terms "comprises" or "having" are intended to indicate that there is a feature, number, step, action, component, part, or combination thereof described on the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof. When a component is said to be "connected" or "connected" to another component, it may be directly connected to or connected to that other component, but it may be understood that other components may be present in the middle. Should be. On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that there is no other component in between.

On the other hand, "module" or "unit" for the components used in the present specification performs at least one function or operation. In addition, the "module" or "unit" may perform a function or an operation by hardware, software, or a combination of hardware and software. In addition, a plurality of "modules" or a plurality of "parts" other than a "module" or a "part" to be performed in specific hardware or performed by at least one control unit may be integrated into at least one module. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In addition, in describing the present invention, when it is determined that a detailed description of related known functions or configurations may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be abbreviated or omitted. Meanwhile, although each embodiment may be independently implemented or operated, each embodiment may be implemented or operated in combination.

2 is a block diagram of a voltage balancer including a DC-DC converter function according to an embodiment of the present disclosure.

Referring to FIG. 2, the voltage balancer 100 including the DC-DC converter function includes a bipolar DC bus unit 110, a DC-DC converter unit 120, and a controller 130. Electricity is transmitted from the power transmission station to the distribution station, and the voltage balancer 100 may receive electricity from the distribution station. A power distribution station implemented with a bipolar distribution network may supply power to a voltage balancer 100 including a DC-DC converter function through three lines of a positive line, a neutral line, and a negative line.

The bipolar DC bus unit 110 is connected to the bipolar power distribution network. That is, the bipolar DC bus unit 110 includes a line connected to the positive terminal, the negative terminal, and the neutral terminal, respectively. The line connected to the positive terminal is the positive line, the line connected to the negative terminal is the negative line, and the line connected to the neutral terminal is the neutral line. As an example, when a voltage of 380V is supplied to the voltage balancer 100, 0V may be applied to the neutral line, 190V to the positive line, and −190V to the negative line.

The DC-DC converter unit 120 is connected in parallel with each line of the bipolar DC bus unit 110 and includes a plurality of switches. The DC-DC converter 120 may supply power to the load.

The DC-DC converter 120 may include a first capacitor connected between the positive terminal and the neutral terminal, and a second capacitor connected between the negative terminal and the neutral terminal. The bipolar DC bus unit 110 may include a first resistor connected in parallel with the first capacitor and a second resistor connected in parallel with the second capacitor. That is, in the voltage balancer 100 including the DC-DC converter function, the first capacitor and the first resistor are connected in parallel between the positive line and the neutral line, and the second capacitor and the second resistor are connected between the negative line and the neutral line. This can be connected in parallel. For example, the first resistor and the second resistor may be resistors included in the voltage balancer 100 including the DC-DC converter function. Alternatively, the first and second resistors may include virtual resistors that may cause an unbalanced voltage situation. For example, the voltage balancer 100 including the DC-DC converter function may be included in a system for charging included in an electric vehicle charging station. The voltage balancer 100 including the DC-DC converter function may be connected to the power distribution network. In addition, the power distribution network may be connected to a system for supplying power to various electronic devices or electronic devices that consume power in an electric vehicle charging station. That is, the distribution network for supplying power to each device (or system) of the EV charging station may be a common network. Therefore, each device (or system) of the EV charging station in terms of the voltage balancer 100 including the DC-DC converter function may be the virtual resistor described above.

The controller 130 balances the magnitude of the first voltage between the positive terminal and the neutral terminal and the magnitude of the second voltage between the negative terminal and the neutral terminal, and simultaneously supplies power to the load. Control the switch. If the first resistance value and the second resistance value are the same, the magnitude of the first voltage and the magnitude of the second voltage are theoretically the same. However, in practice, the magnitude of the first voltage and the magnitude of the second voltage may not be the same due to an error value of the resistance. In addition, as described above, since the first resistor and the second resistor may include virtual resistors, and the virtual resistors may have different values, the magnitude of the first voltage and the magnitude of the second voltage are not the same. You may not. Therefore, the controller 130 may balance and maintain the magnitude of the first voltage and the magnitude of the second voltage by appropriately adjusting the duty ratio according to the magnitude of the first voltage and the magnitude of the second voltage. have.

On the other hand, the load may include an energy storage device such as an electric vehicle or a battery.

Specific circuits and operations of the voltage balancer 100 will be described below.

3 is a circuit diagram of a voltage balancer including a DC-DC converter function according to an embodiment of the present disclosure.

The circuit of the voltage balancer may include a bipolar DC bus unit 110 and a DC-DC converter unit 120. The bipolar DC bus unit 110 includes a line connected to the positive terminal, the negative terminal, and the neutral terminal. Each terminal can be connected to a power distribution network. The input voltage source V _in represents the voltage between the positive electrode p and the negative electrode n being constantly controlled. The bipolar DC bus unit 110 includes a first resistor R ₁ connected in parallel between the positive line and the neutral line, and a second resistor R ₂ connected in parallel between the negative line and the neutral line. The first resistor R ₁ and the second resistor R ₂ may include virtual resistors that may cause an unbalance of voltage.

The DC-DC converter unit 120 is connected in parallel with the bipolar DC bus unit 110. The DC-DC converter unit 120 includes a first capacitor C ₁ connected in parallel between the positive line and the neutral line, and a second capacitor C ₂ connected in parallel between the negative line and the neutral line. That is, the first capacitor C ₁ and the second capacitor C ₂ may be connected in parallel with the first resistor R ₁ and the second resistor R ₂ , respectively.

In addition, the DC-DC converter 120 includes a plurality of switches for controlling the rate of fertilization. The first switch S ₁ may be connected in series to the cathode line, and the second switch S ₂ may be connected in series to the anode line. The third switch S ₃ may be connected in parallel to the neutral line and the cathode line. The third switch S ₃ may be connected to the neutral terminal and one end of the first switch S ₁ . The fourth switch S ₄ may be connected in parallel to the positive line and the negative line. The fourth switch S ₄ may be connected to one end of the first switch S ₁ and _one end of the second switch S ₂ . Additionally, the end of the DC-DC converter 120 includes two inductors (L _1, L ₂₎ and a load capacitor (C _o) comprises, and the DC-DC converter unit 120, and it can be connected to a load (load) . For example, the load may be an energy storage device such as an electric vehicle or a battery.

The voltage balancer of the present disclosure may simultaneously perform the functions of the voltage balancer and the DC-DC converter. If a load is connected, the voltage balancer of the present disclosure may simultaneously perform a voltage balancing function and a power converting function. If the load is not connected, the voltage balancer of the present disclosure may operate only as a voltage balancer.

The operation of the voltage balancer is described below.

4 is a diagram illustrating an operation mode of a voltage balancer including a DC-DC converter function in a state in which a load is not connected according to an embodiment of the present disclosure.

First, a voltage balance state and a voltage unbalance state will be described with reference to FIG. 3. In the circuit of FIG. 3, when the magnitude of the first voltage V _C1 and the magnitude of the second voltage V _C2 are unbalanced, the average unbalanced current I _un may be expressed as follows.

--- (1)

--- (One)

In Equation (1), upper case means the mean value. In order for the bipolar voltages (the first voltage and the second voltage) to be balanced, the average DC component current should not flow through the first capacitor C ₁ and the second capacitor C ₂ . In this case, I _un and the average inductor current I _L must be the same value. For example, under equilibrium conditions (eg, R ₁ = R ₂ ), I _un becomes I _L equals zero and the bipolar voltage maintains equilibrium. However, under unbalanced conditions (eg R ₁ ≠ R ₂ ), I _un will have a specific value and the voltage balancer will operate to equal I _L and I _un .

4 illustrates an operation process when the voltage balancer operates only as the voltage balancer because the load is not connected. In FIG. 4, it is assumed that the bipolar voltage is in equilibrium and that C ₁ = C ₂ and L ₁ = L ₂ . The voltage balancer of the present disclosure adjusts i _{L. cir} to the required value to compensate for the unbalanced voltage and the value of the average current I ₁ should be equal to the value of I _un .

Referring to FIG. 4A, the mode 1 state is shown. In mode 1, the first switch S ₁ and the fourth switch S ₄ are turned on, and the second switch S ₂ and the third switch S ₃ are turned off. v _{L. cir} becomes -V _c2 , i _{L. cir} decreases linearly and flows through the first switch S ₁ and the fourth switch S ₄ . Thus, i ₁ appears as a waveform like i _L.cir .

Referring to FIG. 4B, the mode 2 state is shown. In mode 2, the third switch S ₃ is turned on and the first switch S ₁ is turned off. The second switch S ₂ and the fourth switch S ₄ maintain the previous state. v _{L. cir} becomes 0 and i _{L. cir} flows through the third switch S ₃ and the fourth switch S ₄ . Thus, i ₁ becomes 0.

Referring to FIG. 4C, the mode 3 state is shown. In mode 3, the second switch S ₂ and the third switch S ₃ are turned on, and the first switch S ₁ and the fourth switch S ₄ are turned off. A third switch (S ₃₎ is turned on, though the third, the third switch (S ₃₎ is equal to the off-state does not exist, the current path via the switch (S _3). v _{L. cir} becomes V _c1 and i _{L. cir} increases linearly and flows through the second switch S ₂ . Thus, i ₁ appears as a waveform like i _{L. cir} . The mode 4 state is the same as the mode 2 state.

5 is a diagram illustrating waveforms according to an operation mode of a voltage balancer including a DC-DC converter function when no load is connected.

Referring to FIG. 5, the steady state waveform of the voltage balancer is shown when no load is connected. The ratio d of the first switch S ₁ and the second switch S ₂ is the same and may have a phase difference of 180 degrees. The third switch S ₃ , the first switch S ₁ , and the fourth switch S ₄ may operate complementarily. The voltage balancer of the present disclosure may operate at a specific rate ratio value when operating only as a voltage balancer. For example, the fertilization rate value may have a value between 0.4 and 0.6. In FIG. 5, when the voltage balancer is in a normal state, it may be confirmed that I ₁ has a value equal to I _un, and thus voltage balancing control is performed. I _{L. cir} can be expressed as

--- (2)

--- (2)

If the voltage is unbalanced, the voltage balancer can balance the voltage by adjusting the rate of application. For example, when the first voltage V _C1 is greater than the second voltage V _C2 , the voltage balancer reduces the rate at which the first switch S ₁ is turned on to increase the magnitude of the first voltage V _C1 . And the magnitude of the second voltage V _C2 may be balanced. In addition, when the second voltage V _C2 is greater than the first voltage V _C1 , the voltage balancer increases the rate at which the first switch S ₁ is turned on, thereby increasing the magnitude and size of the first voltage V _C1 . The magnitude of the two voltages V _C2 can be balanced.

Alternatively, when the first voltage V _C1 is greater than the second voltage V _C2 , the voltage balancer increases the rate at which the second switch S ₂ is turned on, thereby increasing the magnitude of the first voltage V _C1 and the first voltage V _C1 . The magnitude of the two voltages V _C2 can be balanced. In addition, when the second voltage V _C2 is greater than the first voltage V _C1 , the voltage balancer reduces the rate of turning on the second switch S ₂ , thereby reducing the magnitude and the first voltage V _C1 . The magnitude of the two voltages V _C2 can be balanced.

Alternatively, when the first voltage V _C1 is greater than the second voltage V _C2 , the voltage balancer increases the rate of turning on the second switch S _{2 and} turns on the first switch S ₁ . By reducing the rate of ratio, the magnitude of the first voltage V _C1 and the magnitude of the second voltage V _C2 may be balanced. In addition, when the second voltage V _C2 is greater than the first voltage V _C1 , the voltage balancer increases the rate of turning on the first switch S _{1 and} turns on the second switch S ₂ . By reducing the rate of ratio, the magnitude of the first voltage V _C1 and the magnitude of the second voltage V _C2 may be balanced.

FIG. 6 is a diagram illustrating waveforms according to an operation mode of a voltage balancer including a DC-DC converter function when a load is connected.

Referring to Figure 6, the steady state waveform of the voltage balancer when the load is connected is shown. The switch of the voltage balancer to which the load is connected can be controlled in the same way as when the load is not connected.

The i _Lo waveform shows that the voltage balancer including the DC-DC converter function performs the charging function. Even if i _Lo is present, I _{L. cir} can be controlled by Eq. (2) by the voltage balancer. As shown in FIG. 6, when the first switch S ₁ and the fourth switch S ₄ are turned on, i ₁ is equal to i _L2 . And, as shown in FIG. 4, I ₁ becomes the same value as I _un, and the bipolar voltage is balanced. The relationship between the average inductor current and I _un from the i ₁ waveform can be expressed as follows.

--- (3)

--- (3)

According to Kirchhoff's law, the relationship between the average output load current I _o and the average inductor current can be expressed as follows.

--- (4)

--- (4)

Using equations (3) and (4), the average inductor current can be obtained as follows.

--- (5)

--- (5)

--- (6)

--- (6)

As described above, in a voltage unbalance state, the voltage balancer may balance the voltage by adjusting the rate of application. For example, when the first voltage V _C1 is greater than the second voltage V _C2 , the voltage balancer reduces the rate at which the first switch S ₁ is turned on to increase the magnitude of the first voltage V _C1 . And the magnitude of the second voltage V _C2 may be balanced. In addition, when the second voltage V _C2 is greater than the first voltage V _C1 , the voltage balancer increases the rate at which the first switch S ₁ is turned on, thereby increasing the magnitude and size of the first voltage V _C1 . The magnitude of the two voltages V _C2 can be balanced.

Alternatively, when the first voltage V _C1 is greater than the second voltage V _C2 , the voltage balancer increases the rate at which the second switch S ₂ is turned on, thereby increasing the magnitude of the first voltage V _C1 and the first voltage V _C1 . The magnitude of the two voltages V _C2 can be balanced. In addition, when the second voltage V _C2 is greater than the first voltage V _C1 , the voltage balancer reduces the rate of turning on the second switch S ₂ , thereby reducing the magnitude and the first voltage V _C1 . The magnitude of the two voltages V _C2 can be balanced.

Alternatively, when the first voltage V _C1 is greater than the second voltage V _C2 , the voltage balancer increases the rate of turning on the second switch S _{2 and} turns on the first switch S ₁ . By reducing the rate of ratio, the magnitude of the first voltage V _C1 and the magnitude of the second voltage V _C2 may be balanced. In addition, when the second voltage V _C2 is greater than the first voltage V _C1 , the voltage balancer increases the rate of turning on the first switch S _{1 and} turns on the second switch S ₂ . By reducing the rate of ratio, the magnitude of the first voltage V _C1 and the magnitude of the second voltage V _C2 may be balanced.

7 is a diagram illustrating a control process of a controller according to one embodiment of the present disclosure.

7 illustrates a control process of the controller 130. The controller 130 may include a module for controlling charging when the load to be charged is connected to the voltage balancer and a voltage balance control module 131 for controlling the balance of the bipolar voltage regardless of the load connection. Since the present disclosure relates to the feature of maintaining the voltage balance, only a process of controlling the balance of the bipolar voltage will be described in FIG. 7.

Since the voltage V _in input to the voltage balancer is assumed to be controlled by the NPC at a constant value, the controller 130 controls only the second voltage V _C2 to a constant value. The voltage balance control module 131 may be implemented as a double PI loop controller in which a V _C2 voltage controller and an i _{L. cir} current controller are connected in series. The voltage balance control module 131 may divide the output signal of the i _{L. cir} current control loop by V _in to finally generate a ratio ratio Δd. The controller 130 may generate modified fertilization ratios d ₁ and d ₂ used for PWM based on the fertilization ratio d and the difference ratio Δd. The control unit 130 the first switch (S ₁₎ and the third switch, the second switch (S ₂₎ and the fourth switch (S ₄₎ based on the control of the (S _3), and d ₂ on the basis of the d ₁ To control.

Hereinafter, the simulation and test results of the voltage balancer of the present disclosure will be described.

8 is a diagram illustrating a simulation result of a voltage balancer including a DC-DC converter function when no load is connected.

8 (a) shows an output waveform of a voltage balancer without a load connected thereto. As a simulation condition, set the input voltage (V _in ) to 400V, the ratio (d) to 0.4, and alternately separate one of the first resistor (R ₁ ) and the second resistor (R ₂ ) for intentional unbalanced load conditions. It became.

The voltage balancer is balanced before 0.2s. At this time, I _{L, cir} is 0 because an unbalance current does not flow. The first resistor R ₁ was separated at 0.2 s. At this time, I _{L, cir} increases through voltage balance control and maintains the value calculated by Equation (2) after the transient state passes. When the first resistor R ₁ is reconnected at 0.3 s, the voltage balancer is in equilibrium, and thus I _{L, cir} becomes zero again. At 0.4 s, the second resistor R ₂ is separated and I _{L, cir} decreases until it reaches the value calculated by equation (2). At 0.5 s, the voltage balancer is in equilibrium when the second resistor R ₂ is reconnected. As shown in FIG. 8A, the voltage balancer of the present disclosure may perform voltage balance control. The voltage balancer can compensate for unbalanced voltages even with zero output power.

FIG. 8B shows an enlarged waveform of 0.25 s of FIG. 8A. It can be seen that the waveform of FIG. 8B is almost the same as the theoretical waveform of FIG. 5.

9 is a diagram illustrating a simulation result of a voltage balancer including a DC-DC converter function when a load is connected.

9A shows an output waveform of a voltage balancer connected to a load. Referring to FIG. 9A, it can be seen that the voltage balancer can maintain an equal voltage even when the first resistor R ₁ and the second resistor R ₂ are unbalanced.

9 (b) shows an enlarged waveform of the 0.06s portion of FIG. 9 (a). In Figure 9 (b) I _Lo is about 3.3A, where V _o is 50V. Therefore, the output power (P _o) is about 165W. That is, the voltage balance method of the conventional TL converter cannot control the voltage balance when unbalanced power (P _un )> output power (P _o ) or P _o = 0, but the voltage balancer of the present disclosure does not have P _un > P _o Voltage balance control can also be performed at. Therefore, the voltage balancer of the present disclosure may have a wider voltage compensation range than the voltage balancing method of the conventional TL converter.

FIG. 10 illustrates an experimental result of a voltage balancer including a DC-DC converter function according to an embodiment of the present disclosure.

Referring to FIG. 10, the voltage balancer of the present disclosure shows the same experimental results as the simulation results. That is, the voltage balancer of the present disclosure can confirm that the first voltage V _C1 is maintained at a constant value while d ₂ is changed little by little in an unbalanced state, and as a result, the bipolar voltages V _C1 and V _C2 are maintained at the same value. .

Although the above has been illustrated and described with respect to preferred embodiments of the present invention, the present invention is not limited to the above-described specific embodiments, it is usually in the art to which the invention belongs without departing from the spirit of the invention claimed in the claims. Various modifications can be made by those skilled in the art, and these modifications should not be individually understood from the technical spirit or prospect of the present invention.

100: voltage balancer 110: bipolar DC bus unit
120: DC-DC converter unit 130: control unit

Claims (6)

A bipolar DC bus unit including lines connected to the positive terminal, the negative terminal, and the neutral terminal, respectively;
A DC-DC converter unit connected in parallel with each line of the bipolar DC bus unit and including a plurality of switches and supplying power to a load; And
Controlling a plurality of switches of the DC-DC converter unit to supply power to the load while balancing a magnitude of a first voltage between the positive terminal and the neutral terminal and a magnitude of a second voltage between the negative terminal and the neutral terminal A voltage balancer including a DC-DC converter function. The method of claim 1,
The DC-DC converter unit,
A first capacitor connected between the positive terminal and the neutral terminal and a second capacitor connected between the negative terminal and the neutral terminal,
The bipolar DC bus unit,
And a DC-DC converter function comprising a first resistor connected in parallel with the first capacitor and a second resistor connected in parallel with the second capacitor. The method of claim 1,
The DC-DC converter unit,
A first switch disposed in series on a line connected to the negative electrode terminal, a second switch disposed in series on a line connected to the positive electrode terminal, a third switch connected to a line connected to the neutral terminal and one end of the first switch, and the A voltage balancer comprising a DC-DC converter function comprising a fourth switch connected to one end of the first switch and one end of the second switch. The method of claim 3,
The control unit,
And a DC-DC converter function to complementarily turn on and off the first switch and the third switch, and to alternately turn on and off the second switch and the fourth switch. The method of claim 4, wherein
The control unit,
And a DC-DC converter function to sequentially turn on and off the first switch and the second switch based on a preset ratio. The method of claim 5,
The control unit,
When the first voltage is greater than the second voltage, a preset ratio of turning on the first switch is reduced to balance the magnitude of the first voltage and the magnitude of the second voltage.
When the second voltage is greater than the first voltage, a DC-DC converter function to balance the magnitude of the first voltage and the magnitude of the second voltage by increasing a preset ratio for turning on the first switch. Including voltage balancer.

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