KR20230139056A - 3 phase 4 wire inverter of independent power supply apparatus for vehicles - Google Patents

Abstract

A 3-phase 4-wire inverter for an independent power supply for a vehicle is disclosed. The 3-phase 4-wire inverter of the independent power supply for a vehicle according to the present invention includes a first capacitor unit for supplying switching ripple current; a second capacitor unit for supplying single-phase load power of a set frequency component; and a switching unit that switches to supply three-phase or single-phase power from the first capacitor unit and the second capacitor unit. Here, the first capacitor part may be implemented as a film capacitor, and the second capacitor part may be implemented as two electrolytic capacitors connected in series.

Description

3-phase 4-wire inverter of independent power supply for vehicles {3 PHASE 4 WIRE INVERTER OF INDEPENDENT POWER SUPPLY APPARATUS FOR VEHICLES}

The present invention relates to a three-phase, four-wire inverter for an independent power supply for a vehicle, and more specifically, to a three-phase, four-wire inverter for an independent power supply for a vehicle that can supply power to not only a three-phase load but also a single-phase load with one inverter configuration. It's about inverters.

Special purpose vehicles such as medical, camping, and military use require an independent power supply device that can replace the grid power source. In particular, military tactical vehicles are equipped with a variety of equipment, but a generator is required because low-voltage batteries cannot supply sufficient power. For this purpose, the inconvenience of previously operating a separate generator trailer was accepted.

Recently, a direct engine-type generator has been developed to enable power generation using the engine in the vehicle itself, and as vehicle systems have changed to electric vehicles, hydrogen vehicles, etc., high-voltage batteries have been installed to provide power supply of tens of kW on their own. Because of this, there is a demand for compact AC power supplies that can be mounted on vehicles.

In particular, military stand-alone power supplies must be capable of supplying three-phase 380Vrms and single-phase 220Vrms at 60Hz. In order to supply three-phase and single-phase power, a three-phase inverter and a single-phase inverter are required. However, when the three-phase inverter and the single-phase inverter are individually configured, there is a problem in that although it has high reliability, it is difficult to construct a compact system.

Public Patent Publication No. 10-2018-0024274 (Publication date: 2018.03.08)

The present invention was created to solve the above-mentioned problems, and its purpose is to provide a three-phase, four-wire inverter for an independent power supply for vehicles that can supply power to not only three-phase loads but also single-phase loads with one inverter configuration. .

In order to achieve the above-described object, a three-phase four-wire inverter of an independent power supply for a vehicle according to one aspect of the present invention includes a first capacitor unit for supplying switching ripple current; a second capacitor unit for supplying single-phase load power of a set frequency component; and a switching unit that switches to supply three-phase or single-phase power from the first capacitor unit and the second capacitor unit.

Here, the first capacitor unit may be implemented as a film capacitor.

Additionally, the second capacitor unit may be implemented by connecting two electrolytic capacitors in series.

The first capacitor unit is implemented with a capacitance that satisfies the ripple current and ripple voltage specifications due to switching based on the following equation.

Here, Icap is the current output from the first capacitor unit, Io is the initial current, m is the modulation index, Φ is the phase angle, fsw is the switching frequency, and Vripple is the ripple voltage.

In addition, the second capacitor unit is implemented as a capacitance for supplying a single-phase load based on the following equation.

Here, Vm is the modulation index voltage, Im is the modulation index current, Vdc is the direct current voltage, Vripple is the ripple voltage, and w is the operating angular frequency.

According to the present invention, one inverter configuration can supply power to not only three-phase loads but also single-phase loads.

Figure 1 is a diagram showing a 3-leg inverter as an example of a 3-phase 4-wire inverter.
Figure 2 is a diagram showing a DC link neutral point connection inverter as an example of a 3-phase 4-wire inverter.
Figure 3 is a diagram showing a DC link neutral point control inverter as an example of a 3-phase 4-wire inverter.
Figure 4 is a diagram showing a 4-leg inverter as an example of a 3-phase 4-wire inverter.
Figure 5 is a diagram showing the principle of neutral point control of 4 legs, where (a) shows 3 legs and (b) shows 4 legs.
Figure 6 is a diagram schematically showing a three-phase, four-wire inverter of a vehicle power supply device according to an embodiment of the present invention.

Hereinafter, some embodiments of the present invention will be described through exemplary drawings. When assigning reference numerals to components in each drawing, identical components are indicated with the same reference numerals as much as possible, even if they are shown in different drawings. Additionally, when describing embodiments of the present invention, if detailed descriptions of related known configurations or functions are judged to impede understanding of the embodiments of the present invention, the detailed descriptions will be omitted.

Additionally, when describing the components of an embodiment 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, coupled, or connected to that other component, but may not be connected to that component or that other component. It should be understood that another component may be “connected,” “coupled,” or “connected” between elements.

Figures 1 to 4 are examples of a 3-phase 4-wire inverter. Figure 1 is a diagram showing a 3-leg inverter, Figure 2 is a diagram showing a DC link neutral point connection inverter, and Figure 3 is a diagram showing a DC link neutral point control inverter. , and Figure 4 is a diagram showing a 4-leg inverter.

A 3-phase 4-wire inverter according to an embodiment of the present invention is used. Compared to using a 3-phase and full-bridge inverter, the 4-leg method can effectively improve unbalanced voltage while reducing semiconductor elements such as IGBT (Insulated Gate Bipolar Transistor), gate drivers, and sensing circuits. Therefore, it is possible to supply three-phase 380Vrms and single-phase 220Vrms.

As a control method for a 4-leg inverter, the control method is converted to a synchronous coordinate system like a typical 3-leg inverter. Under unbalanced conditions, not only DC components but also secondary harmonics appear, and a complex conversion process is required even when compensating for harmonics, making the controller design complicated. It becomes.

In addition, each phase control method to strengthen control under unbalanced conditions has disadvantages such as the use of an all-pass filter, an increase in the number of controllers, and an increase in computation time. However, when controlling in a stationary coordinate system, the 60Hz fundamental wave and the 3rd, 5th, and 7th harmonic components are expressed as is, which has the advantage of simplifying the controller design.

There are various inverter configurations to solve the imbalance problem, including a DC link neutral point connection method that connects the N phase using the neutral point of the DC power supply, a method of controlling the DC link neutral point voltage with an N phase switch, and a load neutral point connection method using an N phase switch. There is a 4-leg method of control.

In the case of the DC link neutral point connection type, the number of elements used is small compared to other configuration methods, so the configuration is simple and additional loss is small, but it has the disadvantage of not being able to control the N-phase current. Additionally, when the load is connected to the neutral point, there is a disadvantage that the capacitor must also handle the load current. Therefore, under unbalanced conditions, a large capacitor capacity is required, and there is a problem that the capacitor voltage may fluctuate or vary depending on the unbalance.

The capacitor neutral point control method, which is a combination of the capacitor neutral point connection type and the 4-leg type, has the advantage of being able to control the capacitor neutral point independently of the 3-phase control and control the voltage fluctuation or split phenomenon of the capacitor, but the 4-leg method Compared to , capacitor voltage sensing is additionally required, and since the neutral point is controlled to 0V, it is difficult to use SVPWM (Space Vector Pulse Width Modulation), which has the problem of lower DC voltage utilization.

In the case of the 4-leg method, N-phase current control is possible through two elements located in the N phase. However, it has the disadvantage of requiring additional elements, but it is possible to control the current on the N phase of the neutral point, thereby enabling unbalanced voltage control, there is almost no ripple in the voltage difference between capacitors, and the SVPWM method can be used to increase the DC link voltage utilization rate. There is an advantage to being able to do this.

Figure 5 is a diagram showing the principle of neutral point control of 4 legs, where (a) shows 3 legs and (b) shows 4 legs.

A three-phase inverter can be assumed to have three single-phase AC power sources, as shown in FIG. 5. In the case of the three-leg method, since the neutral point of the load is not controlled, if the load impedance of each phase becomes unbalanced, the current of each phase and the voltage applied to the load vary. Therefore, the load neutral point has a value other than 0V.

The 4-leg method is the same as connecting the neutral point of the power source and the neutral point of the load. Therefore, the voltage of Vn is maintained equal to 0V, which is the neutral point of the power supply. To this end, the difference in current flowing through each load flows through the neutral line, so three-phase balance can be maintained by controlling the neutral point.

Figure 6 is a diagram schematically showing a three-phase, four-wire inverter of a vehicle power supply device according to an embodiment of the present invention.

Referring to FIG. 6, the 3-phase 4-wire inverter of the vehicle power supply device according to an embodiment of the present invention may include a first capacitor unit 10, a second capacitor unit 20, and a switching unit 30. .

The first capacitor unit 10 is provided to supply switching ripple current. At this time, the first capacitor unit 10 is implemented as a film capacitor with a small equivalent series resistance.

Film capacitors are a common application technology not only for industrial purposes but also for inverter systems. In inverters that control driving motors of electric vehicles, films are used to absorb high-frequency ripple currents through smoothing and switching to remove voltage pulsation components of the DC input voltage stage. Place the capacitor close to the inverter switch and use it at the direct current input terminal.

Meanwhile, when a film capacitor is used alone, it is possible to supply ripple current by switching, but a large capacitance is required to supply power to a single-phase load, and therefore the size of the film capacitor must be increased.

The second capacitor unit 20 is provided to supply power to a single-phase load with a set frequency component. At this time, the second capacitor unit 20 may be implemented by connecting two or more electrolytic capacitors in series. That is, the independent power supply device for a vehicle according to an embodiment of the present invention uses both a film capacitor and an electrolytic capacitor. When an electrolytic capacitor is used alone, a large capacitance is possible, but the size must be increased to supply a large ripple current due to switching.

The purpose of using the 3-phase 4-wire system is to control unbalanced voltage under the same conditions as using 3-phase and single-phase loads simultaneously. At this time, when using three-phase and single-phase loads simultaneously, the capacitor must supply current corresponding to the three-phase load and single-phase load. In the case of a three-phase load, if the three-phase power is calculated for the effective component, it is obtained as follows:

[Equation 1]

Here, Vq and Iq are the voltage value and current value of the q-axis, respectively, and therefore, it can be seen that the power required for the three-phase load is expressed as a DC component.

When a generator is connected to the front end of the DC link, the power supplied from the generator is expressed in the same way, so the power of the three-phase load, which is the DC component, can be supplied from the generator or battery at the front end of the DC link rather than from the capacitor. In other words, the capacitor can be designed to satisfy the ripple current and voltage specifications caused by switching. At this time, a large ripple current is required, but since only the ripple current due to switching is supplied, the capacitance of the film capacitor becomes small. In this case, the capacitor current and capacitance can be designed as shown in Equation 2 and Equation 3.

[Equation 2]

[Equation 3]

Here, Icap is the current output from the combination of the first capacitor unit and the second capacitor unit, Io is the initial current, m is the modulation index, Φ is the phase angle, fsw is the switching frequency, and Vripple is the ripple voltage.

Additionally, the power of a single-phase inverter is expressed as Equation 4.

[Equation 4]

Here, Vm and Im are the modulation index voltage and modulation index current, respectively, and w is the operating angular frequency.

It can be seen that in a single-phase inverter, there is a power ripple of 120Hz, which is a double harmonic of the fundamental wave of 60Hz. At this time, since the power at the front end of the DC link is supplied as DC power, the 120Hz ripple component must be supplied from a capacitor, and therefore a large capacitance is required.

Assuming that the power of the DC side and the AC side are the same in a single phase, the voltage ripple component can be obtained by separating only the AC component from the DC side, and thus the capacitor can be designed according to Equation 5 to Equation 8.

[Equation 5]

Here, Vdc is direct current voltage, Idc is direct current, and Iripple is ripple current.

[Equation 6]

[Equation 7]

[Equation 8]

Here, Vm is the modulation index voltage, Im is the modulation index current, Vdc is the direct current voltage, Vripple is the ripple voltage, and w is the operating angular frequency.

The switching unit 30 switches to supply three-phase or single-phase power from the first capacitor unit 10 and the second capacitor unit 20. That is, the switching unit 30 switches and supplies three-phase or single-phase power based on the capacitance generated by the combination of the first capacitor unit 10 and the second capacitor unit 20.

For example, in FIG. 6, assuming that the capacitance of the film capacitor is C ₁ and that the electrolytic capacitors are C ₂ and C ₃ , respectively, the total capacitance by the film capacitor and electrolytic capacitor can be calculated as Equation 9 You can.

[Equation 9]

At this time, the film capacitor can be designed with a smaller capacitance when used with an electrolytic capacitor than when used alone, and can supply a larger ripple current than when used alone with an electrolytic capacitor.

Although embodiments according to the present invention have been described above, they are merely illustrative, and those skilled in the art will understand that various modifications and equivalent scope of embodiments are possible therefrom. Accordingly, the scope of protection of the present invention should be determined not only by the following claims but also by their equivalents.

Claims (5)

In the 3-phase 4-wire inverter of an independent power supply for a vehicle,
A first capacitor unit for supplying switching ripple current;
a second capacitor unit for supplying single-phase load power of a set frequency component; and
a switching unit that switches to supply three-phase or single-phase power from the first capacitor unit and the second capacitor unit;
A 3-phase 4-wire inverter of an independent power supply for a vehicle, comprising: According to paragraph 1,
A 3-phase 4-wire inverter for an independent power supply for a vehicle, wherein the first capacitor part is implemented with a film capacitor. According to paragraph 1,
A three-phase, four-wire inverter for an independent power supply for a vehicle, wherein the second capacitor part is implemented by connecting two electrolytic capacitors in series. According to paragraph 1,
The first capacitor unit and the second capacitor unit,
A 3-phase 4-wire inverter of an independent power supply for a vehicle, characterized in that it is implemented with a capacitance that satisfies the ripple current and ripple voltage specifications by switching based on the following equation:


Here, Icap is the current output from the first capacitor unit, Io is the initial current, m is the modulation index, Φ is the phase angle, fsw is the switching frequency, and Vripple is the ripple voltage. According to paragraph 1,
The second capacitor part,
A three-phase, four-wire inverter of an independent power supply for a vehicle, characterized in that it is implemented as a capacitance for single-phase load supply based on the following equation:

Here, Vm is the modulation index voltage, Im is the modulation index current, Vdc is the direct current voltage, Vripple is the ripple voltage, and w is the operating angular frequency.