KR102641585B1 - Dc distribution power system and bidirectional converter - Google Patents

Abstract

In one embodiment, N (N is a natural number) energy storage devices; DC bus where direct current voltage is formed; And N bi-directional converters disposed between the DC bus and the energy storage device, wherein the bi-directional converter disconnects the output capacitor from the DC bus when starting, and the voltage of the output capacitor is connected to the DC bus. When the voltage approaches within a certain range, a power system is provided that connects the output capacitor and the DC bus.

Description

DC DISTRIBUTION POWER SYSTEM AND BIDIRECTIONAL CONVERTER}

This embodiment relates to a power system with direct current distribution.

Generally, solar power generators are connected to the grid through AC/DC converters.

Meanwhile, when it is desired to temporarily store power produced by a solar power generator and then transmit it to the grid, an energy storage device including a battery may be used. At this time, the conventional system allows solar power generators and energy storage devices to transmit and receive power via an AC bus or system.

For example, during the power generation period, the solar power generator supplied power to the AC bus through one AC/DC converter, and the energy storage device received power from the AC bus through another AC/DC converter. And, during peak power hours, the energy storage device supplied power to the grid through the AC/DC converter.

This conventional system had poor energy storage efficiency because it had to undergo two AC/DC power conversions. Additionally, since the transmission/reception path includes an AC bus or grid, there was a problem of causing disturbance in the grid when supply and demand did not match. For example, when the power generation of a solar power generator is greater than the charging amount of an energy storage device, the difference is undesirably transferred to the system. And, when the charge amount of the energy storage device is greater than the power generation amount of the solar power generator, the difference is undesirably received from the grid.

Against this background, the purpose of this embodiment is to provide a technology for linking power devices through a DC bus.

In order to achieve the above-described object, one embodiment includes N (N is a natural number) energy storage devices; DC bus where direct current voltage is formed; And N bi-directional converters disposed between the DC bus and the energy storage device, wherein the bi-directional converter disconnects the output capacitor from the DC bus when starting, and the voltage of the output capacitor is connected to the DC bus. When the voltage approaches within a certain range, a power system is provided that connects the output capacitor and the DC bus.

The bidirectional converter includes a first power semiconductor and a second power semiconductor that are controlled synchronously, and may limit the duty of the first power semiconductor within a certain range until certain conditions are met after startup.

The bidirectional converter may operate as a buck converter for power flow to one side and as a boost converter for power flow opposite to the one side.

The first power semiconductor may be disposed between the output terminal of the energy storage device and the inductor, and the second power semiconductor may be disposed between the inductor and ground.

Another embodiment includes a first power semiconductor for chopping an inductor current; a second power semiconductor controlled complementary to the first power semiconductor; an output capacitor disposed at an output terminal of power generated according to on/off of the first power semiconductor and the second power semiconductor; An output switch that controls the connection between the output capacitor and the DC bus; A two-way converter is provided that includes a controller that turns off the output switch during startup and turns on the output switch when the voltage of the output capacitor approaches the voltage of the DC bus within a certain range.

The controller may include a voltage controller and a current controller, and the current controller may generate an on-off signal for the first power semiconductor by comparing the inductor current with a current reference output from the voltage controller.

The controller may limit the current reference to within a first range until a certain condition is met after startup.

The controller may gradually increase the current reference until a certain period of time after startup.

As described above, according to this embodiment, power devices can be connected through a DC bus, thereby increasing the efficiency of power conversion and maintaining the balance between power generation and charging and discharging.

1 is a configuration diagram of a direct current distribution power system according to an embodiment.
Figure 2 is a configuration diagram of a bidirectional converter according to an embodiment.
Figure 3 is a diagram illustrating the configuration of a controller of a bidirectional converter according to an embodiment.
Figure 4 is a configuration diagram of a voltage compensator according to one embodiment.
FIG. 5 is a diagram illustrating a voltage compensator limiting a current reference according to an embodiment.
Figure 6 is a diagram showing main waveforms in a situation where the duty of the first power semiconductor is limited.
Figure 7 is a flowchart of a control method of a bidirectional converter according to an embodiment.
Figure 8 is a configuration diagram of a voltage compensator according to another embodiment.

Hereinafter, some embodiments of the present invention will be described in detail through illustrative drawings. When adding reference numerals to components in each drawing, it should be noted that identical components are given the same reference numerals as much as possible even if they are shown in different drawings. Additionally, in describing the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description will be omitted.

Additionally, when describing the components of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are only used to distinguish the component from other components, and the nature, sequence, or order of the component is not limited by the term. When a component is described as being “connected,” “coupled,” or “connected” to another component, that component may be directly connected or connected to that other component, but there is another component between each component. It will be understood that elements may be “connected,” “combined,” or “connected.”

1 is a configuration diagram of a direct current distribution power system according to an embodiment.

Referring to FIG. 1, the DC distribution power system 100 (hereinafter referred to as 'power system') includes a plurality of DC/DC converters (110a to 110d), a plurality of power devices (10a to 10d), a DC bus 130, and It may include an AC/DC converter 120, etc.

The plurality of power devices 10a to 10d may be, for example, solar power generators, fuel cell generators, energy storage devices, etc.

At least one of the plurality of power devices 10a to 10d may be an energy storage device. Hereinafter, for convenience of explanation, the description will focus on an embodiment in which the first power device 10a is an energy storage device.

The plurality of DC/DC converters 110a to 110d may be one-way converters or two-way converters. In cases where power flow occurs in only one direction, such as in a solar power generator or fuel cell generator, the corresponding DC/DC converter may be a unidirectional converter.

Among the plurality of DC/DC converters 110a to 110d, the DC/DC converter disposed between the energy storage device and the DC bus 130 may be a bidirectional converter. The two-way converter can form a power flow from the energy storage device to the DC bus 130, and can form a power flow from the DC bus 130 to the energy storage device.

Some of the plurality of DC/DC converters (110a ~ 110d) may be one-way converters and others may be two-way converters, but for standardization, all may be composed of two-way converters.

Hereinafter, for convenience of explanation, the description will focus on an embodiment in which the first DC/DC converter 110a is a bidirectional converter.

A direct current voltage may be formed on the DC bus 130. One of the plurality of DC/DC converters 110a to 110d may maintain the voltage of the DC bus 130 at a constant voltage through constant voltage control. For example, the first DC/DC converter 110a connected to the energy storage device can maintain the voltage of the DC bus 130 constant through constant voltage control. At this time, when the voltage of the DC bus 130 increases, the first DC/DC converter 110a can lower the voltage of the DC bus 130 through the charging mode, and when the voltage of the DC bus 130 decreases, the first DC/DC converter 110a can lower the voltage of the DC bus 130. The DC converter 110a can increase the voltage of the DC bus 130 through a discharge mode.

The AC/DC converter 120 can be responsible for transmission and reception between the system and the DC bus 130. For example, the AC/DC converter 120 can convert the DC power formed in the DC bus 130 into AC power and transmit it to the system, and receive AC power from the system and convert it into DC power and then transfer it to the DC bus. It can be supplied as (130).

The power system 100 may further include a higher level controller 140.

The upper controller 140 can receive status information or sense the status from each device that constitutes the power system 100. For example, the upper controller 140 may sense the voltage of the DC bus 130. In addition, the upper controller 140 can receive status information such as state-of-charge (SOC), state-of-health (SOH), and temperature of the energy storage device. In addition, the upper controller 140 can sense the power generation amount of a solar power generator, fuel cell generator, etc. or receive power generation information.

The AC/DC converter 120 and the plurality of DC/DC converters 110a to 110d may include a control circuit - for example, a digital signal processor (DSP) - and the upper controller 140 may be connected to this control circuit. Through communication, the status of each converter can be monitored or control commands can be sent to each converter.

The upper controller 140, the AC/DC converter 120, and the plurality of DC/DC converters 110a to 110d are connected through TCP/IP (transmission control protocol/internet protocol) communication or CAN (controller area network) communication. can be connected through

Figure 2 is a configuration diagram of a bidirectional converter according to an embodiment.

Referring to FIG. 2, the bidirectional converter 210 includes an inductor (L1), an output capacitor (Co), a first power semiconductor (PS1), a second power semiconductor (PS2), a controller 212, and an output switch (SW1). may include.

The two-way converter 210 uses the first power semiconductor (PS1) and the second power semiconductor (PS2) to chop the current formed in the inductor (L1) (hereinafter referred to as 'inductor current') to convert power. It can be converted. For example, the bidirectional converter 210 may chop the inductor current (iL) while repeatedly turning the first power semiconductor (PS1) on and off at regular switching periods (SP: switching period).

The bidirectional converter 210 may be controlled synchronously. For example, when the first power semiconductor (PS1) is turned on, the second power semiconductor (PS2) is turned off, and the first power semiconductor ( When PS1) is turned off, the second power semiconductor PS2 can be turned on. In other words, the first power semiconductor (PS1) and the second power semiconductor (PS2) can be controlled complementary.

The bidirectional converter 210 may operate as a buck converter for power flow to one side and as a boost converter for power flow opposite to one side.

For example, when the node connected to the power device 10 is referred to as the first node (N1) and the node connected to the DC bus 130 is referred to as the second node (N2), the second node (N1) When power flows to the node (N2), the bidirectional converter 210 can operate as a buck converter, and when power flows from the second node (N2) to the first node (N1), the bidirectional converter 210 can operate as a boost converter.

Looking at the arrangement relationship of each component of the bidirectional converter 210 according to this example, a third node (N3) is formed from the inductor (L1) to the power device 10 side, and a fourth node (N4) is formed to the DC bus 130 side. ) can be formed. The first power semiconductor (PS1) may be placed between the power device 10 and the inductor (L1). Looking at the node as the center, it may be placed between the first node (N1) and the third node (N3). . In addition, the second power semiconductor PS2 may be placed between the inductor L1 and the low voltage part - for example, the ground -. Looking at the node as the center, it may be placed between the third node N3 and the low voltage part. You can.

An output capacitor (Co) may be disposed at the output node (N4) in the direction of the DC bus 130. The output capacitor (Co) can perform the function of temporarily storing the inductor current (iL). An input capacitor (not shown) may also be placed at the input node (N1) in the direction of the power device 10. Since power flows in the bidirectional converter 210 in both directions, capacitors can be placed at both the input terminal (N1) and the output terminal (N4).

The bidirectional converter 210 may include an output switch (SW1) that controls the connection between the output node (N4) and the DC bus 130.

When the output switch (SW1) is turned off, the connection between the output node (N4) and the DC bus 130 is released, and when the output switch (SW1) is turned on, the output node (N4) and the DC bus 130 can be connected.

The controller 212 can control the on and off of the first power semiconductor (PS1) by supplying the first on-off signal (PWM1) to the first power semiconductor (PS1), and the second power semiconductor (PS2) The on/off of the second power semiconductor (PS2) can be controlled by supplying the on/off signal (PWM2).

The controller 212 can sense the inductor current (iL) and the voltage (Vo) of the output node (N4), and use the inductor current (iL) and the output voltage (Vo) to generate the first on-off signal (PWM1) and A second on-off signal (PWM2) can be generated.

At startup, the controller 212 turns off the output switch (SW1) to disconnect the output node (N4) and the DC bus 130, and the voltage (Vo) of the output capacitor is constant to the voltage (Vb) of the DC bus. When it approaches within the range, the output switch (SW1) can be turned on.

Figure 3 is a diagram illustrating the configuration of a controller of a bidirectional converter according to an embodiment.

Referring to FIG. 3, the controller 212 may include a voltage controller 310 and a current controller 320.

The voltage controller 310 may include a voltage comparator 312 and a voltage compensator 314. The voltage comparator 312 may compare the output voltage (Vo) and the voltage reference (Vref) and transmit the comparison result to the voltage compensator 314. Here, the comparison result may be the difference between the output voltage (Vo) and the voltage reference (Vref). The voltage compensator 314 may generate a current reference (iref) by compensating the comparison result. The output voltage (Vo) may be a scaled voltage, and the voltage reference (Vref) may also be scaled depending on the scale amount.

The voltage compensator 314 may include a proportional-integral-differential (PID) controller, and the PID controller may include a state variable whose value is accumulated. For example, a PID controller may include an integrator, and the integrator may include state variables.

The current reference (iref) generated by the voltage controller 310 may be transmitted to the current controller 320.

The current controller 320 may include a current comparator 322 and a current compensator 324. The current comparator 322 can compare the inductor current (iL) and the current reference (iref) and transmit the comparison result to the current compensator 324. Here, the comparison result may be the difference between the inductor current (iL) and the current reference (iref). The current compensator 324 can compensate for the comparison results and generate an on-off signal (PWM: pulse width modulation) for the power semiconductor.

Meanwhile, the difference between the output voltage (Vo) and the voltage reference (Vref) may be accumulated in the above-mentioned state variable, and this state variable may cause the current reference (iref) to increase rapidly during startup. For example, if the initial value of the state variable is significantly different from the normal state value, the voltage compensator 314 may rapidly increase the current reference (iref) to quickly transition to the normal state. However, this rapid increase in current reference (iref) causes a rapid increase in the on-time or duty (duty: ratio of on-time to switching cycle) of the first power semiconductor, which eventually causes saturation of the inductor or It can induce overcurrent in power semiconductors.

To improve this problem, the controller 212 may limit the duty of the first power semiconductor to within a certain duty range or limit the current reference to a certain current range until certain conditions are met after startup. As one technique for this limitation, the controller 212 may gradually increase the current reference (iref) until a certain period of time after startup.

Figure 4 is a configuration diagram of a voltage compensator according to one embodiment.

Referring to FIG. 4, it may include a compensation circuit 410, a limiting circuit 420, and a mux circuit 430.

The compensation circuit 410 may generate a first current reference (iref1) by performing compensation processing (for example, PID compensation processing) on the difference between the voltage reference and the output voltage. When the limit is not applied, the first current reference (iref1) and the current reference (iref) may have the same value.

The limiting circuit 420 may generate a second current reference (iref2) whose value gradually increases until a certain period of time after startup.

Also, the mux circuit 430 can select one of the first current reference (iref1) and the second current reference (iref2) and output the current reference (iref). For example, the mux circuit 430 may select the smaller value of the first current reference (iref1) and the second current reference (iref2) and output it as the current reference (iref), and the first current until a certain time after startup. Among the reference (iref1) and the second current reference (iref2), the second current reference (iref2) can be selected and then the first current reference (iref1) can be selected for output.

FIG. 5 is a diagram illustrating a voltage compensator limiting a current reference according to an embodiment.

In Figure 5, the first current reference (iref1) may rapidly increase due to the difference between the output voltage and the voltage reference during startup. On the other hand, the value of the second current reference (iref2) gradually increases up to a certain time according to a predetermined time function and can maintain a constant value thereafter.

The current reference (iref) may be composed of the smaller value of the first current reference (iref1) and the second current reference (iref2). According to this, it initially follows the second current reference (iref2) and then follows the first current reference (iref2). You can follow (iref1). After a certain period of time has elapsed, the first current reference (iref1) may become lower than the second current reference (iref2) because the voltage compensator reaches a steady state.

On the other hand, according to this control, excessive increase in duty of the first power semiconductor can be prevented within a certain time after startup, but the second power semiconductor, which is controlled complementary to the first power semiconductor in the two-way converter, is controlled in the initial period - for example. For example, it may be damaged due to overcurrent in the period from start to the first time (T1). The reason for such damage will be described later with reference to FIG. 6.

To prevent damage to the second power semiconductor, the controller disconnects the output capacitor and the DC bus after startup until certain conditions are met, and when the voltage of the output capacitor approaches the voltage of the DC bus within a certain range - For example, at the second time (T2), the output capacitor and the DC bus can be connected.

Figure 6 is a diagram showing main waveforms in a situation where the duty of the first power semiconductor is limited.

Referring to FIG. 6, the duty DT1 of the on-off signal PWM1 of the first power semiconductor may be limited to a certain duty LV or less until a certain condition is satisfied after startup.

At this time, the duty DT2 of the on-off signal PWM2 of the second power semiconductor, which is controlled complementary to the first power semiconductor, may be relatively long.

In the on-section of the first power semiconductor, the inductor current (iL) may increase, and then in the on-section of the second power semiconductor, the inductor current (iL) may decrease. Depending on the embodiment, on the contrary, the inductor current (iL) may decrease in the on-section of the first power semiconductor and then increase in the inductor current (iL) in the on-section of the second power semiconductor. Below, the former example will be described for convenience of explanation.

Meanwhile, since the duty (DT1) of the on-off signal (PWM1) of the first power semiconductor is limited to a certain duty (LV) or less during startup, the duty (DT2) of the second power semiconductor is formed to be relatively long, and thus the inductor current For (iL), the decrease becomes larger than the increase. And, if this phenomenon accumulates every switching cycle (SP1 to SP3), the inductor current (iL) may generate an excessively large current in the second power semiconductor and damage the second power semiconductor.

To prevent such burnout, the controller releases the connection between the output capacitor and the DC bus after startup until a certain condition is satisfied, and when the voltage of the output capacitor approaches the voltage of the DC bus within a certain range - for example, 2 hours (T2)-, can be connected between the output capacitor and the DC bus.

Figure 7 is a flowchart of a control method of a bidirectional converter according to an embodiment.

Referring to FIG. 7, the bidirectional converter can be started while limiting the duty of the on-off signal (PWM1) of the first power semiconductor (S702).

Also, when the bidirectional converter is started, the output switch that controls the connection between the output terminal and the DC bus can be turned off (open) (S704).

In addition, the bidirectional converter can control the voltage (output voltage) of the output capacitor to a preset voltage by supplying inductor current to the output capacitor in a no-load state.

And, the two-way converter compares the output voltage and the voltage of the DC bus (bus voltage) (S708), and when the output voltage approaches the bus voltage within a certain range (YES in S708), it turns on the output switch to connect the output terminal and the DC bus. It can be connected, or if not (NO in S708), additional power conversion can be performed by keeping the output switch in the off state until the output voltage approaches the bus voltage.

Figure 8 is a configuration diagram of a voltage compensator according to another embodiment.

Referring to FIG. 8, the voltage compensator 810 may include a compensation circuit 810, a soft start capacitor (Css), and a soft start switch (SWss).

The comparison result between the voltage reference and the output voltage may be transmitted to the compensation circuit 810. Additionally, the compensation circuit 810 may generate a current reference (iref) according to compensation processing - for example, PID processing - for the comparison result.

At this time, the compensation circuit 810 can turn on the soft start switch (SWss) during startup to connect the soft start capacitor (Css) in parallel to the internal integration capacitor. Depending on this connection, the integral gain increases and the rate of increase of the current reference (iref) may be limited.

And, the compensation circuit 810 can turn off the soft start switch (SWss) after a certain condition is satisfied.

As described above, according to this embodiment, power devices can be connected through a DC bus, thereby increasing the efficiency of power conversion and maintaining the balance between power generation and charging and discharging.

Terms such as “include,” “comprise,” or “have,” as used above, mean that the corresponding component may be included, unless specifically stated to the contrary, and do not exclude other components. It should be interpreted that it may further include other components. All terms, including technical or scientific terms, unless otherwise defined, have the same meaning as generally understood by a person of ordinary skill in the technical field to which the present invention pertains. Commonly used terms, such as terms defined in a dictionary, should be interpreted as consistent with the meaning in the context of the related technology, and should not be interpreted in an idealized or overly formal sense unless explicitly defined in the present invention.

The above description is merely an illustrative explanation of the technical idea of the present invention, and various modifications and variations will be possible to those skilled in the art without departing from the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but are for illustrative purposes, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be interpreted in accordance with the claims below, and all technical ideas within the equivalent scope should be construed as being included in the scope of rights of the present invention.

Claims (8)

N (N is a natural number) energy storage devices;
DC bus where direct current voltage is formed; and
It includes N two-way converters disposed between the DC bus and the energy storage device,
The two-way converter is,
A first power semiconductor for chopping the inductor current, a second power semiconductor controlled complementary to the first power semiconductor, and formed according to the on/off of the first power semiconductor and the second power semiconductor. An output capacitor disposed at the output terminal of the power, an output switch disposed between the output capacitor and the DC bus and controlling the connection between the output capacitor and the DC bus, and turning off the output switch when starting, and the output capacitor When the voltage approaches the voltage of the DC bus within a certain range, it includes a controller that turns on the output switch to control the connection between the output capacitor and the DC bus,
The controller is,
Includes a voltage controller and a current controller,
The current controller is,
Generating an on-off signal for the first power semiconductor by comparing the current reference output from the voltage controller with the inductor current,
The controller is,
After starting, limit the current reference to within a first range until certain conditions are met,
The controller is,
Gradually increasing the current reference until a certain period of time after startup,
Power system. According to paragraph 1,
The two-way converter is,
A power system that limits the duty of the first power semiconductor within a certain range after startup until certain conditions are met. According to paragraph 2,
The two-way converter is,
A power system that operates as a buck converter for power flow to one side and as a boost converter for power flow opposite to the one side. According to paragraph 2,
The first power semiconductor is disposed between the output terminal of the energy storage device and the inductor,
A power system in which the second power semiconductor is disposed between the inductor and ground. delete delete delete delete

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