KR20160147575A - Power Converter for Charging Battery of Electric Vehicle - Google Patents

Abstract

The present invention relates to a power converter for charging a battery of an electric vehicle (EV). More specifically, the present invention relates to a power converter for charging a battery of an electric vehicle, which integrates an LLC series resonant converter to a conventional phase shift full converter. According to the present invention, the power converter has the effect of widening a zero voltage switching operation range, reducing the size of a filter inductor, and reducing voltage stress of a rectification diode. Also, the present invention has the effect of increasing battery charging efficiency since power conversion efficiency is increased.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a power converter for charging a battery of an electric vehicle,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for charging a battery of an electric vehicle (EV), and more particularly, to an LLC serial resonant converter (LLC Series Resonant) in a conventional phase shift full bridge converter Converter for charging an EV battery.

The global market for electric vehicles was estimated to reach 16,000 cars in 2010, but in 2015, it will surpass 1 million. The development of environmentally friendly vehicles as a substitute for depleted fossil fuels is becoming a big issue.

Automobiles using electric power as a propulsion power are essentially used batteries, and a battery charger for charging the battery must be an essential device in such an electric automobile application.

An on-board battery charger in an EV application is comprised of a power factor corrector for harmonic regulation and an isolated DC-DC converter for battery charging, The battery charger directly charges the battery of the electric vehicle from the output of the power factor correction circuit.

Among the various algorithms for battery charging of electric vehicles, the CC-CV algorithm (constant current-constant voltage algorithm) is most effective and powerful and widely applied to charger applications. In the CC-CV algorithm, the output voltage of the DC-DC converter of the on-board battery charger changes greatly in the CC charging period, and the output load in the CV charging period decreases to almost no load at full load. The above-described operating characteristics make it difficult to design an optimal DC-DC converter in terms of power conversion efficiency.

For example, conventional phase-shifted full bridge converters have a narrow zero voltage switching range of lagging-leg switches that are inherent defects, large circulating currents on the primary side of the transformer, ) And rectifying diodes, the high power conversion efficiency in the CC-CV charging algorithm could not be achieved. Resonant converters, such as series resonant converters, have had similar problems due to the very wide variation in switching frequency in the charging of electric vehicle batteries.

Korean Patent Laid-Open No. 10-2009-0098473 (disclosed on September 17, 2009)

The present invention provides a power converter for charging an electric automobile battery incorporating an LLC serial resonant converter in a conventional phase shift full bridge converter in order to improve the efficiency of charging an electric automobile battery There is a purpose.

According to an aspect of the present invention, there is provided a power converter for charging a battery of an electric vehicle, comprising: a converter switching unit having four switches for switching an input voltage and a first transformer connected between the four switches; An LLC serial resonant converter unit connected to the converter switching unit to convert the input voltage; And an energy recovering unit for rectifying and outputting the voltage converted by the LLC series resonant converter unit, wherein the converter switching unit has a structure in which the four switches are of a full bridge structure, Bridge structure and has a winding on the secondary side of the first transformer.

In addition, the converter switching unit performs a switching operation using a phase shift method, and the switch is a MOSFET.

The LLC serial resonant converter unit includes the second transformer, the first inductor, and one capacitor, one end of which is connected to a contact between two switches installed in the same direction, and the other end is connected to the ground .

The energy recovery unit includes two diodes connected in series in the same direction; Two capacitors connected in series; And the second transformer having one end connected to a contact between the two diodes and the other end connected to a contact between the two capacitors, wherein the two diodes and the two capacitors are connected in parallel.

According to the present invention, the zero voltage switching operation range is widened, the size of the filter inductor is reduced, the circulating current is reduced, and the voltage stress of the rectifier diode can be reduced.

In addition, according to the present invention, the power conversion efficiency is increased, and battery charging efficiency is also increased.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram illustrating a configuration of a power converter for charging a battery of an electric vehicle according to an embodiment of the present invention; FIG.
2 is a diagram showing a theoretical operating waveform of a power converter for charging a battery of an electric vehicle according to an embodiment of the present invention;
FIGS. 3A through 3E illustrate driving modes of a power converter for charging a battery of an electric vehicle according to an embodiment of the present invention; FIGS.
4A to 4D illustrate operation results of a power converter for charging a battery of an electric vehicle actually manufactured according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a configuration diagram illustrating a configuration of a power converter for charging a battery of an electric vehicle according to an embodiment of the present invention.

As shown in FIG. 1, a power converter for charging a battery of an electric vehicle according to an embodiment of the present invention includes a converter switching unit, an LLC serial resonant converter unit, and an energy recovery unit.

The converter switching unit includes four switches Q1, Q2, Q3 and Q4 for switching the input voltage and a first transformer T1 connected between the four switches Q1, Q2, Q3 and Q4. The four switches (Q1, Q2, Q3, Q4) have a full bridge structure, the first transformer is disposed between the full bridge structures, and the secondary side of the first transformer has one winding structure Respectively. The converter switching unit performs a switching operation using a phase shift method. A MOSFET can be used as the switch. This is because, when MOSFETs are used, both zero voltage and zero current switching are possible. However, this is merely an example and the use of the switch is not limited thereto.

The LLC series resonant converter unit is connected to the converter switching unit to convert the input voltage. The LLC series resonant converter includes a second transformer T2, a first inductor Lr, and a capacitor Cr. As shown in Fig. 1, one end is connected to a contact between two switches Q3 and Q4 installed in the same direction, and the other end is connected to a ground.

The energy recovery unit rectifies the voltage converted by the LLC serial resonant converter unit and outputs the rectified voltage. The energy recovery unit may include two diodes D5 and D6, two capacitors Cf1 and Cf2, and a second transformer T2.

The two diodes D5 and D6 are connected in series in the same direction and the two capacitors Cf1 and Cf2 are connected in series and the two diodes D5 and D6 and the two capacitors Cf1 and Cf2 are connected in series. Are connected in parallel. At this time, the second transformer T2 is connected at one end to a contact between the two diodes D5 and D6 and at the other end to a contact between the two capacitors Cf1 and Cf2.

Because of the integration of the converter switching part and the LLC series resonant converter part, the lagging-leg switch is very easily reached to the zero voltage switching, and the zero voltage switching becomes independent from the output load condition. Due to the energy recovery, all rectifier diodes in the converter switching section are turned off with zero current switching. And the commutation diodes of the LLC series resonant converter section are under the zero current switching operation. Furthermore, since the main current of the converter switching unit is reset to 0 [A] during the freewheeling phase interval, the circulating current that is present in the conventional phase shifting full bridge converter is minimized.

The secondary rectifier circuit of the full bridge converter with energy recovery is placed in series with the secondary rectifier circuit of the LLC series resonant converter. With the above configuration, the voltage stress of all rectifier diodes can be limited below 300V in an electric vehicle 3.3kW on-board battery charger application and the utilization of the two transformers is improved compared to conventional hybrid converters.

Hereinafter, the operation principle of the power converter for charging the battery of the electric vehicle according to the embodiment of the present invention will be described with reference to FIG. 2 and FIG.

2 is a diagram showing a theoretical operational waveform of a power converter for charging a battery of an electric vehicle according to an embodiment of the present invention.

As shown in FIG. 2, the power converter according to the embodiment of the present invention has the same driving signal for switch activation as the conventional phase-shift full-bridge power converter. And the output is controlled in a phase shift manner like the conventional phase shifted full bridge power converter.

FIGS. 3A through 3E are views illustrating a driving mode of a power converter for charging a battery of an electric vehicle according to an embodiment of the present invention.

The power converter for charging the battery of the electric vehicle according to the present invention has 20 operating modes in the switching period. In mode 1, mode 10 (t0 to t10), mode 11 to mode 20 (t10 to t20) And can be divided into two half cycles. Since the two half cycles are symmetrical, only one half cycle of the mode 1 to the mode 10 will be described below as shown in FIGS. 3A to 3E.

Mode 1: Mode 1 starts when switch Q1 and switch Q3 are turned on. In mode 1, since Vp1 (t) has a (+) input voltage, the battery charge current flows through the diodes D1 and D3, the capacitors Cf1 and Cf2, the clamp capacitor Cc, the auxiliary diode Da2, the output inductor Lo and the first transformer T1 Flow. It can be seen from the power path that the converter switching unit and the LLC series resonant converter deliver the power required at the output terminal together.

The resonant current of the LLC series resonant converter part charges the capacitor Cf1 through the diode D5 in the same time period. The rectifier output voltage Vrec (t) is the sum of the voltage applied to Cc and the output voltage Vo.

이라면, 제 1변압기 T1의 주 전압은 하기의 수학식 1을 통해 얻을 수 있다.If the output voltage of the LLC series resonant converter is

, The main voltage of the first transformer T1 can be obtained by the following equation (1).

The main current ip1 (t) in the converter switching part can be expressed by the following equation (2).

The mode 1 ends when the switch Q1 is turned off.

Mode 2: Mode 2 starts when the switch Q1 is turned off at t1. Since the battery charge current still flows through D1 and D3 and the main current has a maximum value, Q1 or Q2 is very easily charged or discharged according to the following equation (3).

Vp1 (t) decreases linearly to 0 [V] as VQ2 (t) quickly. And Vrec (t) maintains the same value as the value in mode 1. The resonant current of the LLC series resonant converter section continuously charges Cf1. The mode 2 section is very narrow and the time interval of the mode 2 may be omitted in explaining the principle of the power converter according to the present invention.

는 모드 1 또는 모드 2에서와 같이 동일한 값을 가진다. 그리고

는 역으로 T1의 주 누설 인덕터(leakage inductor)

에 인가된다. 그러면 주 전류 ip1(t)는 하기의 수학식 4의 기울기를 가지고 선형적으로 줄어들기 시작한다. Mode 3: Mode 3 starts when Vp1 (t) reaches 0 [V]. During mode 3, the voltage applied between Q2 is zero. Thus, the switch Q2 turns on with zero voltage switching.

Has the same value as in Mode 1 or Mode 2. And

Is the reverse leakage inductor of T1,

. Then, the main current ip1 (t) begins to decrease linearly with the slope of the following equation (4).

The currents of the diode Da2 and the diode D1 also linearly decrease with the slope of the following equation (5).

The mode 3 ends when the diode Da2 is turned off together with the zero current switching.

에 인가된다. 그리고 ip1(t)가 하기의 수학식 6의 기울기에 따라서 선형적으로 감소하기 시작한다. 그 결과, 다이오드 D1, D3 와 다이오드 Da1 사이에서 커뮤테이션(commutation)이 일어난다. 그리고 Vrec(t)는 Cc 사이의 전압과 LLC 직렬 공진 컨버터 부의 출력전압의 합이 된다. 이는 하기의 수학식 6에서와 같다. Mode 4: Mode 4 starts when the diode Da2 is turned off and the diode Da1 conducts. The voltage of Cc

. Then, ip1 (t) starts to decrease linearly according to the slope of the following equation (6). As a result, commutation occurs between the diodes D1 and D3 and the diode Da1. And Vrec (t) is the sum of the voltage between Cc and the output voltage of the LLC series resonant converter. This is shown in Equation (6) below.

At the end of Mode 4, the diodes D1 and D3 are turned off under zero current switching.

Mode 5: Mode 5 begins when diodes D1 and D3 are turned off and the battery charge current flows only through diode Da1. Then, ip1 (t) becomes 0 [A], and the converter switching unit stops the powering operation for charging the battery. This means that the battery charge power is supplied only from the output of the LLC series resonant converter section. Mode 5 ends when the resonant current of the LLC series resonant converter section stops charging Cf1 through D5. At the same time, diode D5 turns off with zero current switching.

In the converter switching section controlled by the phase shift method, the freewheeling phase appears when Vp1 (t) is 0 [V]. During the freewheeling phase interval, a non-powering current, often referred to as a circulating current, always flows at the primary side of the first transformer T1 of the converter switching section. This cycling current has been noted for reasons of obvious deficiencies of conventional phase shifting full bridge converters for battery charger applications. This is because the cycling current was always present in wide-output-voltage applications such as battery chargers, and the conduction current increased the conduction power loss. In particular, the conduction power loss caused by the circulating current is maximized when the battery voltage becomes the minimum value. Because in that situation the freewheeling phase interval is very long.

On the other hand, in the present invention, when Vp1 (t) becomes 0 [V], the main current ip1 (t) is reset to 0 [A] as described in modes 3 and 4. And no current flows to the primary side. This means that the circulating current that is present in the conventional phase shift full bridge is removed. As a result, the conduction power loss at the primary side of the transformer can be greatly reduced during the entire battery charging process.

Mode 6: Mode 6 starts when diode D5 is turned off. The battery charge power is supplied from the output of the LLC series resonant converter section. The main current ip2 (t) becomes the magnetizing current of the second transformer T2. At the end of the mode 6, the switch Q3 is turned off.

에 저장된 에너지에 의하여 하기 수학식 7에 따라서 충전되거나 방전된다. Mode 7: Mode 7 starts when switch Q3 is turned off. At the same time, Q3 or Q4 is the magnetizing inductor of T2

Is charged or discharged according to the following equation (7).

Vp1 (t) begins to decrease to the negative input voltage. The mode 7 ends when Vp1 (t) reaches the voltage of Cc having a turn-ratio of T1.

에 도달할 때 시작한다. 다이오드 D2와 D4는 도통하기 시작하고, 다이오드 D2와 D4 그리고 Da1 사이에서 커뮤테이션이 발생한다. Vrec(t)는 그 전의 값으로 유지되기 때문에, D2와 D4의 전류는 하기 수학식 8의 기울기로 증가하기 시작하고, Da1의 전류는

에서부터 감소하기 시작한다. Mode 8: In mode 8, Vp1 (t) is

Lt; / RTI > Diodes D2 and D4 begin to conduct, and commutation occurs between diodes D2 and D4 and Da1. Since Vrec (t) is maintained at the previous value, the currents of D2 and D4 start to increase by the slope of the following expression (8), and the current of Da1 becomes

Lt; / RTI >

According to Equation (8), Vp1 (t) continues to decrease toward the negative input voltage.

에 도달하고, 다이오드 Da1은 영전류 스위칭 아래 턴 오프 된다. Mode 9: Mode 9 starts when Vp1 (t) reaches the negative input voltage. Then the voltage between switch Q4 is 0 [V], and Q4 turns on with zero voltage switching. The resonance between Lr and Cr occurs again on the primary side of the LLC series resonant converter section and the resonant current of the LLC series resonant converter section starts charging the capacitor Cf2 through the diode D6. In mode 9, since diodes D2 and D4 continue to communicate with Da1, Vrec (t) has the same value as the value in mode 8. At the end of mode 9, the currents of diodes D2 and D4

And the diode Da1 is turned off under zero current switching.

와 Vo의 합이고, ip1(t)는 상기 수학식 2의 기울기를 가지고 감소한다. 상기 LLC 직렬 공진 컨버터 부의 공진 전류는 Cf2를 계속해서 충전한다. Mode 10: Mode 10 starts when the commutation is fully established between diodes D2 and D4 and Da1. At the same time, the diode Da2 begins to conduct. As a result, both the converter switching unit and the LLC series resonant converter unit begin to charge the battery, which is described in Mode 1 above. In this mode 10, Vrec (t)

And Vo, and ip1 (t) decreases with the slope of Equation (2). The resonant current of the LLC series resonant converter section continues to charge Cf2.

Since the operation from the subsequent mode 11 to the mode 20 is symmetrical with the half cycle from the mode 1 to the mode 10, the operation for one half cycle from the mode 1 to the mode 10 is maintained from the mode 11 to the mode 20 I would say.

Hereinafter, an actual configuration and a driving result of a power converter for charging a battery of an electric vehicle according to another embodiment of the present invention will be described with reference to FIGS. 4A to 4D.

In order to demonstrate the effect of the power converter for charging a battery of an electric vehicle according to the present invention, a 3.3 kW prototype circuit is manufactured through the devices shown in Table 1 below, and a CC- .

The prototype circuit can be set to have an input voltage VIN = 400V, an output voltage Vo = 250-420V, a charging current IBattery = 7.85A in the CC mode, and a switching frequency fs = 100kHz. However, the present invention is not limited to the above-mentioned conditions.

Components

characteristic
The main switch (Q1-Q4)

IPP60R074C6 (650V)
The rectifier diodes D1, D2, D3, D4,

LQA10T30 (300V)
The rectifying diodes D5 and D6,

B40250TG (250V, Schottky diode)
The diodes Da1,

B40250TG (250V, Schottky diode)
Transformer (T1)
Core-PQ5050, Turns-ratio (n1) -0.585
Lm-1.13mH, Llk-5.4uH
Transformer (T2)
Core-PQ3535, Turns-ratio (n2) -0.5
Lm-120uH, Llk -3.95uH
Resonant inductor Lr,

17.75uH
The resonant capacitor (Cr)

100nF / 630V
Clamp capacitor (Cc)

1uF / 250V
Output inductor (Lo)

250 uH (MPP core)
Output capacitors (Cf1, Cf2)

4.7uF / 250V (Low ESR firm capacitor)
Output capacitor (Co2)

450uF / 500V
Controller

TMS320F28027

4A shows a core drive waveform of the power converter according to the present invention while the battery is being charged to a constant current of 7.85A from 250V to 420V. As shown in Fig. 4A, all the measured operation waveforms are the same as the theoretical operation waveforms in Fig. Furthermore, when the main voltage Vp1 (t) becomes zero in the process of charging the battery, the power converter according to the present invention has a reduced circulating current on the primary side of the transformer. Also, it can be confirmed that the output voltage is continuously transmitted from the converter switching unit to the energy recovery unit through the stepwise voltage waveform of the output voltage Vrec of the rectifier. It can be seen that the size of the output filter inductor is smaller than that of the conventional phase shift full bridge converter.

Figures 4B and 4C show the zero voltage switching waveform of the lagging leg switch during battery charging. As shown in Figures 4b and 4c, due to the combination with the LLC resonant converter portion, the lagging leg switch from no load condition to full load condition is successfully turned on with zero voltage switching.

Figure 4d shows the charge efficiency measured during the battery charging process in CC mode (7.85A) and CV mode (420V). As shown in Figure 4d, the power converter according to the present invention exhibits better performance than conventional phase shifting full bridge converters due to reduced circulating current, wider zero voltage switching range, zero current switching operation of all rectifier diodes, and lower winding ratio .

The power converter according to the present invention exhibits efficiencies up to 98.09% under full load conditions.

The embodiments of the present invention described in the present specification and the configurations shown in the drawings relate to the most preferred embodiments of the present invention and are not intended to encompass all of the technical ideas of the present invention so that various equivalents It should be understood that water and variations may be present. Therefore, it is to be understood that the present invention is not limited to the above-described embodiments, and that various modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims. , Such changes shall be within the scope of the claims set forth in the claims.

Claims (5)

A converter switching part including four switches connected in a full bridge structure for switching an input voltage and a first transformer disposed between the full bridge structure;
An LLC serial resonant converter unit connected to the converter switching unit to convert a voltage input to the converter switching unit; And
And an energy recovery unit for rectifying and outputting the voltage converted by the LLC series resonant converter unit,
Wherein the secondary side of the first transformer is a structure having one winding. The method according to claim 1,
Wherein the converter switching unit performs a switching operation using a phase shift method. 3. The method of claim 2,
Characterized in that the switch is a MOSFET. The method according to claim 1,
The LLC series resonant converter unit includes:
A second transformer, a first inductor, and a capacitor,
Wherein one end is connected to a contact between two switches installed in the same direction and the other end is connected to a ground. 6. The method of claim 5,
The energy recovery unit includes:
Two diodes connected in series in the same direction;
Two capacitors connected in series; And
The second transformer having a first end connected to a contact between the two diodes and a second end connected to a contact between the two capacitors,
Wherein the two diodes and the two capacitors are connected in parallel.

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