Seven-switch indirect matrix converter with passive secondary circuit

Abstract

A direct current (DC) fast charger for charging a battery of an electric vehicle (EV) includes a primary circuit having seven bidirectional switches electrically linked to a primary wire of a transformer and configured to receive an alternating current (AC) voltage; and a secondary circuit comprising a plurality of diodes arranged to rectify the AC voltage into a DC voltage, electrically linked to the secondary leads of the transformer such that the DC fast charger unidirectionally converts the AC voltage received at the primary circuit into the DC voltage output by the secondary circuit.

Description

Government interests

[0001] This invention was made with government support under Contract DE-EE0009869 awarded by the U.S. Department of Energy, Directorate of Energy Efficiency and Renewable Energy EE-1. The U.S. Government has certain rights in this invention. Technical Field

[0002] The present application relates to electric vehicles (EVs), and more particularly to chargers for charging EVs. Background Art

[0003] Modern vehicles are increasingly propelled at least partially or entirely by electric motors. A vehicle, often referred to as an electric vehicle (EV), includes a vehicle battery and one or more electric motors that drive the vehicle wheels. The vehicle battery is periodically coupled to a battery charger. As drivers purchase increasing numbers of EVs, they will want to be able to charge the vehicle battery relatively quickly. Therefore, faster and more efficient vehicle battery chargers are helpful. Summary of the invention

[0004] In one implementation, a direct current (DC) fast charger for charging a battery of an electric vehicle (EV) includes: a primary circuit having seven bidirectional switches electrically linked to a primary conductor of a transformer and configured to receive alternating current (AC) power; and a secondary circuit including a plurality of diodes arranged to rectify the AC power into DC power, the secondary circuit being electrically linked to the secondary conductor of the transformer so that the DC fast charger unidirectionally converts the AC power received at the primary circuit into DC power output by the secondary circuit.

[0005] In another implementation, a DC fast charger for charging a battery of an EV includes: a primary circuit, which includes seven bidirectional switches electrically linked to a primary conductor of a transformer and configured to receive AC power; a secondary circuit, which includes a full-bridge rectifier, which includes passive electrical components arranged to rectify AC power into DC power, the full-bridge rectifier being electrically linked to the secondary conductor of the transformer, wherein the DC fast charger unidirectionally converts AC power received at the primary circuit into DC power output by the secondary circuit.

[0006] In yet another implementation, a DC fast charger for charging a battery of an EV includes: a primary circuit comprising seven bidirectional switches electrically linked to a primary conductor of a transformer and configured to receive AC power; a spacer inductor electrically connected to the primary circuit; a secondary circuit comprising a full-bridge rectifier and a capacitor, the full-bridge rectifier comprising passive electrical components arranged to rectify AC power into DC power, the full-bridge rectifier and the capacitor electrically linked to the secondary conductor of the transformer, wherein the DC fast charger unidirectionally converts AC power received at the primary circuit into DC power output by the secondary circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a block diagram depicting the implementation of an electric vehicle;

[0008] Figure 2 is a circuit diagram depicting the implementation of a DC fast charger and control system; and

[0009] 3a-3f are circuit diagrams depicting implementations of a DC fast charger. DETAILED DESCRIPTION

[0010] A seven-switch indirect matrix converter DC fast charger for vehicle applications is unidirectional, such that it converts electrical power received from the grid and supplies the converted power to an electric vehicle (EV) to charge the vehicle (G2V). The DC fast charger includes a primary circuit having a seven-switch topology that includes bidirectional switches. The secondary circuit of the DC fast charger is able to use a passive diode bridge rather than actively controlled switches, such as those with gates that adjust conductivity, thereby reducing cost relative to other designs. The electrical power supplied to the DC fast charger is three-phase AC electrical power.

[0011] A seven-switch indirect matrix converter or DC fast charger can deliver unidirectional electrical power from a three-phase grid at a primary circuit to a secondary circuit by controlling the modulation of a half-square wave. In one implementation, a three-phase AC voltage grid cycle measured in 1 / 50-1 / 60 seconds (s) can be divided into a plurality of (e.g., six) sectors, each sector being marked by two consecutive AC zero voltage inflection points. In each sector, the phase with the highest absolute value can be designated as the leading phase, and the other two phases can be used to apply a controlled voltage to the primary circuit. The current applied to the primary circuit can then include three different duty cycles, each corresponding to the voltage. D x Capable of marking voltage V a -V bThe duty cycle of the primary circuit can be identified, Dy can identify the duty cycle of the voltage Va-Vc, and D0 can identify the duty cycle of the phase idling when the seventh switch is active. The seventh switch can facilitate a 50% reduction in conduction losses during an idling period under a light electrical load. The current applied to the primary circuit can be converted into DC power by a diode bridge of the secondary circuit. The secondary circuit can include an inductor and a capacitor to smooth the DC electrical output from the secondary circuit.

[0012] Go to Figure 1 , shows an implementation of an electrical system 10, which includes a power grid 12 and an electric vehicle (EV) 14, which can receive electric power from the grid 12 or provide electric power to the grid 12. The power grid 12 can include any one of several electric power generators and power transmission mechanisms. A generator (not shown) produces AC electric power, which can then be transmitted a considerable distance away from the generator for residential and commercial use. The generator can be coupled to the power grid 12, and the power grid 12 transmits the AC electric power from the generator to an end user, such as a residence or a business. When the AC electric power is provided to the power grid 12, the electric power can exist at a relatively high voltage, so that it can be transmitted over a relatively long distance. Once the electric power reaches the location where it is expected to be used, a power transformer (not shown) can be used to reduce the voltage level before it is finally provided to a residence or business. In one implementation, the voltage level of the AC electric power used is 360-510 volts RMS alternating current three-phase 50-60Hz. However, the voltage range can be different.

[0013] The EV charging station (referred to herein as a DC fast charger 16) can receive AC electric power from the power grid 12, rectify the AC electric power into DC electric power, and provide the DC electric power to the EV 14. The DC fast charger 16 can be geographically fixed, such as a charging station located in a vehicle garage or in a vehicle parking lot. The DC fast charger 16 can include an input terminal that receives AC electric power from the power grid 12 and transfers the AC electric power directly to the EV battery 22, thereby bypassing the onboard vehicle battery charger 18 included on the EV 14. The cable 20 can be detachably connected to an electrical socket on the EV 14 and electrically links the DC fast charger 16 with the EV 14 so that DC electric power can be transferred between the DC fast charger 16 and the EV battery 22. The DC fast charger 16 can receive 480VAC from the power grid 12 and has a rated power of 60-360kW provided to the EV 14. This type of DC fast charging can be referred to as Level 3 EV charging. However, EV charging stations can use different standards. The term "electric vehicle" or "EV" can refer to a vehicle that is propelled in whole or in part by an electric motor. EV can refer to an electric vehicle, a plug-in electric vehicle, a hybrid electric vehicle, and a battery-powered vehicle. The EV battery 22 can supply DC electric power controlled by power electronics to the electric motor that propels the EV. One or more EV batteries 22 are rechargeable and can include lead-acid batteries, nickel-cadmium (NiCd), nickel-metal hydride, lithium-ion, and lithium-polymer batteries. A typical range of vehicle battery voltage can vary from 100 to 1000V DC electric power (VDC). A control system implemented as computer-readable instructions executable by a microprocessor can be stored in a non-volatile memory and called to control the functionality of the DC fast charger 16. This will be discussed in more detail below.

[0014] Figure 2An implementation of a DC fast charger 16 and a control system 24 for use with the charger 16 is depicted. The DC fast charger 16 is an indirect matrix converter that includes a primary circuit 26 and a secondary circuit 28 that are inductively coupled together via a transformer 30. The primary circuit 26 includes seven switches 32 that are electrically coupled to the grid 12 and the primary winding 34 of the transformer 30. The switches 32 can be implemented using bipolar junction transistors (BJTs) or field effect transistors (FETs) such as insulated gate bipolar transistors (IGBTs), metal oxide semiconductor field effect transistors (MOSFETs), or gallium nitride transistors (GaN). The switches 32 can be bidirectional or reverse blocking, such that they are four-quadrant switches that can conduct positive or negative on-state currents and block positive or negative off-state voltages. Such switches can be implemented using a number of different circuit configurations, any of which can be implemented in the DC fast chargers described herein. In one implementation, each switch 32 includes an A-side MOSFET and a B-side MOSFET having a gate that can be electrically connected to a microprocessor. The six switches 32a-f can be electrically coupled to three branches PHA, PHB, PHC of the power grid and nodes a, b, c of the primary circuit 26. The voltages of these three branches can be identified as V a 、V b and V c The seventh switch 32g can be wired in parallel with the switches 32e and 32f and in parallel with the primary winding 34 of the transformer 32. The inductor 36 and the bulk capacitor 38 can be electrically connected to the branches PHA, PHB, PHC of the grid 12.

[0015] The secondary circuit 28 is electrically connected to the secondary winding 40 of the transformer 32. The circuit 28 includes a passive full-bridge rectifier that can be implemented using four diodes D1-D4. The diodes in the secondary circuit 28 can be implemented using any of a variety of different types of diodes. The secondary circuit 28 can include an electrical filter having an inductor and a capacitor to smooth the output DC voltage. The EV battery 22 can be electrically connected to the diodes so that the secondary circuit 28 passively rectifies the AC voltage induced by the secondary winding 40 into a DC voltage applied to the EV battery 22.

[0016] The control system 24 can be implemented using a microprocessor having an output electrically connected to a gate 42 of the switch 32 in the DC fast charger 16. An implementation of the control system 24 is shown in FIG. 3. The control system 24 includes a phase-locked loop 44 electrically connected to the three legs PHA, PHB, PHC of the grid 12. The phase-locked loop 44 can be used to determine the phase (θ) of the AC voltage received from the grid 12. 电网 This phase can then be provided to the dq transform block 46 to obtain a rotated reference frame (dq ) signal. The voltage controller 48 can use the measured DC voltage level (V dc *-V dc ) to generate the target DC voltage level q *. Ability to q * together with d q are provided to the first current controller 50 to generate V q *. Ability to d * together with d q are provided to the second current controller 52 to generate V d *. The dq-abc block 54 can convert Vq*, Vd* and phase (θ 电网 ) minus the angle offset is received by a voltage source inverter (VSI) space vector modulation (SVM) block 56. The VSI SVM block 56 can provide an output to a current source inverter (CSI) SVM block 58, which can provide an output to a matrix SVM block 60. A gate signal can be generated at block 62 and electrically delivered to the gate of the switch 32 to control the conduction state.

[0017] The DC fast charger 16 can control the primary circuit 26 to cause the AC current to flow in the transformer 30. Changes in the conductivity of the switches 32 included in the primary circuit 26 are shown in Figures 3a-f. The initial switching state of the primary circuit 26 is shown in Figure 3a, where the A MOSFET and the B MOSFET of the switches 32a and 32d are initially conductive to allow current to flow through the branches A and B. The current paths and switch conductivity are shown with arrows and / or hash lines. As shown in Figure 3b, the first switching step can cause the A-side MOSFETs of the switches 32a and 32d to be non-conductive. As shown in Figure 3c, the second switching step can cause the B-side MOSFET of the seventh switch 32g to be conductive. The third switching step is shown in Figure 3d, so that the B-side MOSFET of the switch 32a is rendered non-conductive, the B-side MOSFET of the switch 32c is rendered conductive, and the B-side MOSFET of the switch 32d is rendered non-conductive. The changes in the conductive state of the switches 32a, 32c, and 32d can be considered as soft switching events because they are performed in the absence of current. FIG3e depicts a fourth switching state, in which the B-side MOSFET of switch 32g is rendered non-conductive. A fifth switching state is shown in FIG3f, in which the A-side MOSFET of switch 32c is rendered conductive and the A-side of switch 32b is rendered conductive. The control system 24 can then return the conductive state of the primary circuit 26 to the initial switching state and repeat the five switching states to change the frequency of the AC voltage received from the grid 12.

[0018] It is to be understood that the foregoing is a description of one or more embodiments of the present invention. The present invention is not limited to the (one or more) specific embodiments disclosed herein, but is instead defined only by the claims hereinafter. In addition, except where terms or phrases are clearly defined above, the statements contained in the foregoing description relate to specific embodiments and are not to be interpreted as limitations on the scope of the present invention or on the definition of the terms used in the claims. Various other embodiments and various changes and modifications to the disclosed (one or more) embodiments will become apparent to those skilled in the art. All such other embodiments, changes and modifications are intended to fall within the scope of the appended claims.

[0019] As used in this specification and claims, the terms "for example," "for example," "such as," and "similar," and the verbs "comprise," "have," "include," and other verb forms thereof, when used in conjunction with a list of one or more components or other items, are each to be interpreted as open-ended, meaning that the list is not to be construed to exclude other additional components or items. Other terms are to be interpreted using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.

Claims

1. A direct current (DC) fast charger for charging a battery of an electric vehicle (EV), comprising: a primary circuit including seven bidirectional switches electrically linked to the primary conductor of the transformer and configured to receive an alternating current (AC) voltage; as well as A secondary circuit includes a plurality of diodes arranged to rectify an AC voltage into a DC voltage, the plurality of diodes being electrically linked to the secondary conductors of the transformer, wherein the DC fast charger unidirectionally converts the AC voltage received at the primary circuit into a DC voltage output by the secondary circuit.

2. The DC fast charger of claim 1 , further comprising a control system electrically linked to the seven bidirectional switches, the control system varying the frequency of the AC voltage received from the power grid in five switch state changes.

3. The DC fast charger according to claim 1, wherein the primary circuit uses the primary wire of the transformer as a leakage inductor.

4. The DC fast charger of claim 1, wherein the secondary circuit comprises an inductor and a capacitor.

5. The DC fast charger of claim 1 , further comprising a control system that divides the three-phase AC voltage received at the primary circuit into a plurality of sectors, each of the plurality of sectors being defined by two consecutive inflection points at which the AC voltage is equal to zero.

6. The DC fast charger of claim 5, wherein the control system identifies the sector having the highest absolute voltage.

7. A direct current (DC) fast charger for charging a battery of an electric vehicle (EV), comprising: a primary circuit including seven bidirectional switches electrically linked to the primary conductor of the transformer and configured to receive an alternating current (AC) voltage; a secondary circuit comprising a full-bridge rectifier including passive electrical components arranged to rectify an AC voltage into a DC voltage, the full-bridge rectifier being electrically linked to a secondary conductor of the transformer, wherein the DC fast charger unidirectionally converts an AC voltage received at the primary circuit into a DC voltage output by the secondary circuit.

8. The DC fast charger of claim 7, further comprising a control system electrically linked to the seven bidirectional switches, the control system varying the frequency of the AC voltage received from the power grid in five switch state changes.

9. The DC fast charger according to claim 7, wherein the primary circuit uses the primary wire of the transformer as a leakage inductor.

10. The DC fast charger of claim 7, wherein the secondary circuit comprises an inductor and a capacitor.

11. The DC fast charger of claim 7, further comprising a control system that divides the three-phase AC voltage received at the primary circuit into a plurality of sectors, each of the plurality of sectors being defined by two consecutive inflection points at which the AC voltage is equal to zero.

12. The DC fast charger of claim 11, wherein the control system identifies the sector having the highest absolute voltage.

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