SINGLE PHASE SINGLE STAGE BI-DIRECTIONAL LEVEL 1 ELECTRIC VEHICLE BATTERY CHARGER

Abstract

A single phase single stage level-1 electric vehicle (EV) battery charger can control the power flow in both directions. The converter efficiency is high as the devices undergo ZCS which reduces switching loss in the devices. This converter does not require any intermediate DC link capacitor stage and the power density of the converter is high.

Description

BACKGROUND

This application is a continuation of and claims priority to U.S. patent application Ser. No. 16/638,620, entitled “Single Phase Single Stage Bi-Directional Level 1 Electric Vehicle Battery Charger,” filed Feb. 12, 2020, which is a 371 National Stage Patent Application of and claims priority to International Application No. PCT/US2018/044930, filed Aug. 2, 2018, which claims benefit and priority to U.S. Provisional Patent Application Ser. No. 62/546,955, entitled “Single Phase Single Stage Bi-Directional Level 1 Electric Vehicle Battery Charger,” filed Aug. 17, 2017, the entire contents of which are hereby incorporated by reference.

This disclosure pertains to an electric vehicle (EV) battery charging application.

The electrification of transportation has significantly increased in recent times to reduce fossil fuel consumption and greenhouse emissions. Electric vehicles (EVs) are gradually replacing the conventional internal combustion engine based vehicles. However, the increasing penetration of these EVs can have a considerable impact on the grid. Thus the chargers used for charging the batteries should have additional features like power factor correction (PFC) controllers and bidirectional power flow capabilities to minimize the impact of power quality on the grid.

Commercially available single-phase isolated AC-DC EV battery chargers can be classified into two-stage solution and single-stage solution. The two stage solution consists of a front-end PFC stage. It is followed by an isolated DC-DC stage. The frontend stage employs diode bridge rectifiers followed by a boost, buck, or buck-boost stages. Large storage elements like electrolytic capacitors are required to link these two stages. The main advantage of this two-stage solution is that the output voltage regulation and PFC control are decoupled. Thus, the PFC performance can always be ensured despite the change in input AC voltage and load power. This PFC operation enhances the power quality of the grid. Nevertheless, this two-stage solution suffers from low overall efficiency due to more number of devices. Moreover, the converter power density is limited because of the two separate stages and bulky DC link capacitors.

The alternative solution is to develop single stage AC-DC converters. The fly back converters are selected to achieve cost-effective designs because theoretically only one active switch is necessary. However, they are only suitable for lower power level because of the high-voltage and current stresses on the devices. For high-power rating single stage AC-DC converters, full bridge (FB) type topologies are preferred. In the resonant type FB and dual active bridge type FB AC-DC converters, the output voltage regulation is realized either by changing the switching frequency or by shifting the phase angle between the two bridges. These converters only use capacitors as the output filter. Thus, the voltage rating of the capacitors is lower. However, the main disadvantage of these converters is the nonlinear relation between the control parameters and the input current. Even if a complex control algorithm is applied, the grid current total harmonics distortion (THD) is large compared to conventional two-stage solution.

SUMMARY

The present disclosure relates generally to a battery charger for electric vehicles (EVs), and particularly to a single stage single phase power converter for EV charging application.

In preferred embodiments, the AC side of the proposed converter has a current-fed full bridge matrix converter that is connected to another full-bridge converter on a secondary side of a high-frequency (HF) transformer. The advantages of the proposed EV charger are its bidirectional power flow capabilities, inherent power factor correction (PFC) control, the fact that intermediate DC link capacitors are not required, soft switching capabilities in both primary and secondary side switches, improved grid current quality due to input line inductor, and the fact that the power density and efficiency of the converter is high.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows converter topology for a preferred embodiment of a single phase, single stage level-1 bidirectional electric vehicle (EV) charger.

FIG. 2 shows a preferred embodiment of a converter in Mode 1 of operation during grid to vehicle (G2V) mode.

FIG. 3 shows a preferred embodiment of a converter in Mode 2 of operation during G2V mode.

FIG. 4 shows a preferred embodiment of a converter in Mode 3 of operation during G2V mode.

FIG. 5 shows a preferred embodiment of a converter in Mode 4 of operation during G2V mode.

FIG. 6 shows a preferred embodiment of a converter in Mode 9 of operation during vehicle to grid (V2G) mode.

FIG. 7 shows a preferred embodiment of a converter in Mode 10 of operation during V2G mode.

FIG. 8 shows a preferred embodiment of a converter in Mode 11 of operation during V2G mode.

FIG. 9 shows a preferred embodiment of a converter in Mode 12 of operation during V2G mode.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present disclosure relates to a single phase, single stage level-1 electric vehicle (EV) charger. The single phase single stage level-1 EV battery charger can control the power flow in both directions. Preferred switching sequences of the devices are also described. The converter efficiency is high as the devices undergo ZCS which reduces switching loss in the devices. This converter does not require any intermediate DC link capacitor stage. As an advantage, the power density of the converter is high.

FIG. 1 shows converter topology for a preferred embodiment of a single phase, single stage level-1 bidirectional electric vehicle (EV) charger having inherent PFC control. The primary AC side includes 8 silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) labeled M_1a to M_4b and the secondary side includes 4 SiC MOSFETs labeled M₅ to M₈. The converter develops a high frequency AC in the primary side of the isolating transformer, operating as a cycloconverter. It is then rectified in the secondary side to generate DC voltage. Similar operation is conducted in reverse direction for reverse power flow. Zero current switching (ZCS) is achieved with the help of a resonating circuit that includes leakage inductance (L_k) of the transformer and an external capacitor (C_k).

The converter topology shown in FIG. 1 is a preferred embodiment that can be extended to various applications. The proposed topology can be extended for grid integration of photovoltaic cells. It can operate independently in both grid connected mode and islanded mode. The proposed EV charger topology can also be extended for bidirectional power flow with a three phase operation.

FIG. 2 shows a preferred embodiment of a converter during mode of operation that is grid to vehicle (G2V) mode. In this mode, which may be referred to as Mode 1, power is transferred from the input source (Vin) to the battery (Vbat). For G2V operation, active switching is conducted in the primary side and the secondary side devices are operated as a diode bridge rectifier. For positive input voltage (Vin>0), the operation can be divided from Mode 1 to Mode 4. Similarly, the operation can be divided from Mode 5 to Mode 8 for Vin<0. In this mode M_1a, M_2a are kept on and M_1b and M_2b are kept off. As a result, the input current flows from the source (V_in) to leakage inductor (L_k) and capacitor (C_k) through M_1a, M_2a and diodes of M_1b and M_2b. In the secondary side, diodes of M₅ and M₆ conduct to charge the battery (V_bat).

FIG. 3 shows a preferred embodiment of a converter in Mode 2 of G2V mode. In Mode 2, Device M_4a is turned on and then M_2a is turned off. As a result, ZCS occurs for M_2a. In this case, the input current (I_in) freewheels through M_1a, M_4a and diodes of M_1b and M_4b. The capacitor C_k and inductor L_k starts resonating. This resonance causes the leakage current through L_k to reach input current level. As a result, a voltage spike does not appear across the primary device. In other words, the C_k acts as a snubber capacitor. It helps in arresting the voltage overshoot caused due to the current mismatch between the leakage inductor and line inductor. At the end of Mode 2, M_3a is turned on. It exhibits ZCS turn-on.

FIG. 4 shows a preferred embodiment of a converter in Mode 3 during G2V mode. In Mode 3, M_1a is turned off. The input current flows through M_3a, M_4a and diodes of M_3b and M_4b. The current direction reverses in the leakage inductor L_k and C_k. In the secondary side, diodes of M₇ and M₈ conduct to charge the battery (V_bat).

FIG. 5 shows a preferred embodiment of a converter in Mode 4 during G2V mode. In this mode, M_2a is turned on and then M_4a is turned off. As a result M_4a experiences ZCS turn-off. In this case, the input current (I_in) freewheels through M_3a and M_2a. The capacitor C_k and inductor L_k starts resonating. This resonance causes the leakage current through L_k to reach input current level similar to Mode 2. As a result, a voltage spike does not appear across the primary device. This helps in arresting the voltage overshoot caused due to the current mismatch between the leakage inductor and line inductor. At the end of Mode 3, M_1a is turned on. It exhibits ZCS turn-on.

During V_in>0, Mia, M_2a, M_3a and M_4a exhibit ZCS. In a similar fashion, Mode 5 to Mode 8 can also be explained. Here M_1b, M_2b, M_3b and M_4b exhibit ZCS. It is important to notice that C_k continues to conduct current even if V_bat>V_in. As a result, there is a path for the input current to flow at every switching condition. This phenomena ensures PFC for all loading conditions.

In vehicle to grid (V2G) mode, power is transferred from the battery (V_bat) to the grid (V_in). For V2G operation, battery side devices are switched in square wave mode and three level sine triangle pulse-width modulation (PWM) switching is conducted for the grid side devices. For positive input voltage (V_in>0), the operation can be divided from Mode 9 to Mode 12. Similarly, the operation can be divided from Mode 13 to Mode 16 for V_in<0. For V2G operation, the resonating capacitor C_k is removed from the circuit through a contactor.

FIG. 6 shows a preferred embodiment of a converter in Mode 9 during V2G mode. In this mode, M₅ and M₆ in the secondary side are kept on. The grid current flows through M_1b, M_2b and diodes of M_1a and M_2a.

FIG. 7 shows a preferred embodiment of a converter in Mode 10 during V2G mode. In Mode 10, M_4b is turned on. As a result, the grid current freewheels through M_4b, M_1b and diodes of M_1a and M_4a. M_2b is turned off once the grid current is completely transferred to the freewheeling branch exhibiting ZCS turn-off. At the end of this mode M_3b is turned on. M_3b experiences ZCS turn on as there is no current through it.

FIG. 8 shows a preferred embodiment of a converter in Mode 11 during V2G mode. In Mode 11, M_1b is turned off. As a consequence, grid current flows through M_4b, M_3b and diodes of M_4a and M_4a respectively. This switching cycle reverses the direction of current flowing through the leakage inductor (L_k).

FIG. 9 shows a preferred embodiment of a converter in Mode 12 during V2G mode. At the end of mode 11, M_2b is turned on again. The grid current again freewheels through M_2b, M_3b and diodes of M_2a and M_3a. After the transfer of grid current to the freewheeling branch, M_4b is turned off. It exhibits ZCS turn-off.

Mode 9 to Mode 12 are continued until M₅ and M₆ are in the on-state in the secondary side. Once M₇ and M₈ are turned on, the switching cycles described above are reversed. In a similar fashion, the switching of the devices are carried out for V_in<0. As described above, all devices on the primary side undergo ZCS.

REFERENCES

The following documents and publications are hereby incorporated by reference.

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Claims

1. A power converter having bidirectional power flow capabilities and inherent power factor correction (PFC) control, comprising:

a high frequency transformer comprising a primary AC side, a secondary side, and a resonating circuit,

wherein the primary AC side of the high frequency transformer comprises a current-fed full bridge matrix converter, wherein the current-fed full bridge matrix converter comprises eight silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) positioned in four pairs, wherein a first pair of SiC MOSFETS consists of a first A SiC MOSFET and a first B SiC MOSFET, wherein a second pair of SiC MOSFETs consists of a second A SiC MOSFET and a second B SiC MOSFET,

wherein a third pair of SiC MOSFETs consists of a third A SiC MOSFET and a third B SiC MOSFET, and wherein a fourth pair of SiC MOSFETs consists of a fourth A SiC MOSFET and a fourth B SiC MOSFET,

wherein the secondary side of the high frequency transformer comprises a full bridge matrix converter, wherein the full bridge matrix converter comprises four SiC MOSFETs, wherein the four SiC MOSFETs consist of a fifth SiC MOSFET, a sixth SiC MOSFET, a seventh SiC MOSFET, and an eighth SiC MOSFET, and

wherein the resonating circuit comprises a leakage inductor of the high frequency transformer and a capacitor.

2. An electric vehicle (EV) battery charger comprising the power converter of claim 1.

3. The electric vehicle (EV) battery charger of claim 2, further comprising an input source and a battery.

4. One or more photovoltaic cells comprising the power converter of claim 1.