JP2024081102A - Electric Propulsion System - Google Patents

Abstract

[Problem] To provide an electric propulsion system having a transformer for voltage conversion. [Solution] The electric propulsion system has a motor drive circuit 20 supplied with power from a high-voltage battery 1, and the motor drive circuit drives a propulsion motor. A pair of input terminals of the motor drive circuit are connected to a smoothing capacitor 2. The electric propulsion system further has a battery circuit having a transformer 13 having three or more coils. The transformer is built into a charger 11 for charging the high-voltage battery, and has a battery heating coil 5 for heating the high-voltage battery. The battery heating coil forms a closed loop circuit together with the high-voltage battery and the smoothing capacitor. For example, when a high-frequency secondary voltage is induced in a one-turn battery heating coil, high-frequency power circulates through the high-voltage battery and the smoothing capacitor. As a result, the high-voltage battery is heated. [Selected Figure] Figure 2

Description

The present invention relates to an electric propulsion system, and more particularly to an electric propulsion system having a transformer for voltage conversion.

Electric vehicles (EVs) are known as electric propulsion systems that use the power energy of a high-voltage battery to drive a traction motor. Furthermore, electric ships and electric aircraft are known as electric propulsion systems that use the power energy of a high-voltage battery to drive a propulsion motor. The DC power of the high-voltage battery is converted to AC power by a motor drive circuit and supplied to the propulsion motor. A three-phase inverter is a typical motor drive circuit, but motor drive circuits that further include a boost chopper are also known.

A conventional electric propulsion system has multiple battery circuits connected to a high-voltage battery in addition to a motor drive circuit. The operating voltage of these battery circuits is usually different from the rated voltage of the high-voltage battery. For this reason, each of these battery circuits has a transformer to change the voltage.

One example of a battery circuit is a grid charger that charges a high-voltage battery with grid power. Another example of a battery circuit is a DC-DC converter that transfers battery power from a high-voltage battery to a low-voltage battery.

An example of a conventional electric propulsion system is shown in FIG. 1. A high-voltage battery 1 is substantially connected in parallel to a smoothing capacitor 2 through a wiring box 10. The smoothing capacitor 2 absorbs switching noise of a motor drive circuit 20.

The wiring box 10 has a relay circuit 3, a grid charger 11, a DCDC converter 12, and a controller 30. The relay circuit 3 has system relays 31 and 34, a precharge relay 32, and a resistor 33.

The positive terminal B+ of the high-voltage battery 1 is connected to the positive terminal C+ of the smoothing capacitor 2 through the system relay 31. The negative terminal B- of the high-voltage battery 1 is connected to the negative terminal C- of the smoothing capacitor 2 through the system relay 34.

The grid charger 11 has a grid-side converter 9, a transformer 13, and a battery-side converter 4. The transformer 13 has coils 8A and 7 wound around a soft magnetic core 13A. The grid-side converter 9 consists of a rectifier 93, a capacitor 92, and an oscillator 91.

The rectifier 93 rectifies the single-phase grid voltage to charge the capacitor 92. The capacitor 92 supplies DC power to the oscillator 91, which applies a high-frequency voltage to the coil 7 of the transformer 13. The secondary voltage induced in the coil 8A of the transformer 13 is rectified by the battery-side converter 4A. The battery-side converter 4A, which is connected to the high-voltage battery 1 through the safety relays 35 and 36, applies the rectified voltage to the high-voltage battery 1.

The DCDC converter 12 consists of a battery-side converter 4B, a transformer 14, and a rectifier 61. The transformer 14 has coils 8B and 6 wound around a soft magnetic core 14A. The battery-side converter 4B, connected to the high-voltage battery 1 through safety relays 35 and 36, supplies high-frequency current to the coil 8B. The secondary voltage induced in the coil 6 is rectified by the rectifier 61. The rectified voltage charges the low-voltage battery 60.

On the other hand, in order to improve the performance of the high-voltage battery 1, a battery heating circuit with a transformer that supplies AC power to the high-voltage battery 1 has been proposed. After all, conventional electric propulsion systems have battery circuits with built-in transformers, such as a grid charger, a DCDC converter, and a battery heating circuit. However, these transformers increase the weight of the electric propulsion system.

Patent Document 1 proposes a battery heating circuit that uses a grid charger's transformer as an inductor. According to Patent Document 1, the number of transformers can be reduced. However, Patent Document 1 requires the addition of multiple semiconductor power switching elements in order to use the transformer coil as an inductor. These semiconductor power switching elements that handle high voltages and large currents are expensive.

CN Patent 111181208

The first object of the present invention is to provide an electric propulsion system having a simple power switching circuit and a lightweight transformer.

According to a first aspect of the present invention, a battery circuit associated with an electric propulsion system that drives a propulsion motor has a transformer having three or more coils wound around a common soft magnetic core. This allows multiple operating modes of the electric propulsion system to be implemented using a single transformer, so that the battery circuit has a simple circuit configuration. Furthermore, the total weight of the transformer can be reduced.

In a preferred embodiment, the electric propulsion system operates in at least two of the grid charging mode, the DC-DC converter mode, and the battery heating mode through a common transformer.
In a preferred embodiment, the electric propulsion system operates in grid charging mode, DC-DC converter mode, and battery heating mode all through a common transformer.

According to a second aspect of the present invention, a transformer of an electric propulsion system that drives a propulsion motor has a battery heating coil for passing a secondary current to a high-voltage battery. The battery heating coil, the high-voltage battery, and the smoothing capacitor form a closed loop circuit in which the secondary current circulates. The smoothing capacitor is connected to an input terminal of the motor drive circuit. This makes it possible to realize rapid heating of the high-voltage battery with a simple circuit configuration.

FIG. 1 is a block circuit diagram showing a battery circuit of a conventional electric propulsion system. FIG. 2 is a block circuit diagram showing a battery circuit of the electric propulsion system according to the first embodiment. FIG. 3 is a circuit diagram showing an example of a battery circuit shown in FIG. 2 . 3 is a circuit diagram showing another example of the battery circuit shown in FIG. 2. FIG. 11 is a block circuit diagram showing a battery circuit of an electric propulsion system according to a second embodiment. FIG. 6 is a circuit diagram illustrating a flux sum mode of the battery circuit shown in FIG. FIG. 6 is a circuit diagram showing a magnetic flux difference mode of the battery circuit shown in FIG. 5 .

A battery circuit associated with the electric propulsion system of the present invention will be described with reference to the drawings. However, the technical concept of the present invention may be realized by other known circuit technologies. Furthermore, the electric propulsion system of the present invention includes, in addition to electric vehicles (BEVs), hybrid vehicles (HVs), plug-in hybrid vehicles (PHVs), battery-powered ships (BSs), and battery-powered aircraft (BPs), etc.

First embodiment An electric propulsion system of a first embodiment will be described with reference to Fig. 2. This electric propulsion system, which includes a three-phase inverter 20 that drives the traction motor of an EV, is the same as the conventional electric propulsion system shown in Fig. 1, except for the battery heating coil 5.

The electric propulsion system shown in FIG. 2 has a high-voltage battery 1, a smoothing capacitor 2, and a wiring box 10. The high-voltage battery 1 is a lithium-ion battery with a rated voltage of approximately 400 V. The smoothing capacitor 2, which is a film capacitor with a capacitance of approximately 0.4 mF, is connected to a pair of DC power supply terminals of a motor drive circuit 20. This motor drive circuit 20 is made up of a three-phase inverter, but can also include a boost chopper circuit for boosting the voltage of the smoothing capacitor 2.

The high-voltage battery 1 and the smoothing capacitor 2 are connected through a wiring box 10. The wiring box 10 has a relay circuit 3, a grid charger 11, a DCDC converter 12, and a controller 30. The relay circuit 3 has system relays 31 and 34, a precharge relay 32, a resistor 33, and safety relays 35 and 36.

The positive terminal B+ of the battery 1 is connected to the positive terminal C+ of the smoothing capacitor 2 through the relay 31. The negative terminal B- of the battery 1 is connected to the negative terminal C- of the smoothing capacitor 2 through the relay 34 and the battery heating coil 5. The battery heating coil 5 connects the negative terminal C- of the smoothing capacitor 2 to the system relay 34. The series-connected relay 32 and low resistor 33 are connected in parallel to the system relay 31. As is well known, the relay 32 is turned on before the relay 31. This reduces the current that charges the smoothing capacitor 2.

The grid charger 11, which charges the battery 1 using grid power, consists of a grid-side converter 9, a transformer 13, and a battery-side converter 4A. The grid-side converter 9 consists of a rectifier 93, a capacitor 92, and an oscillator 91.

When the grid voltage is applied to the rectifier 93, the grid charging mode is initiated. In other words, the grid charging mode is executed after the rectifier 93 of the grid-side converter 9 is connected to the electric grid. Before the grid charging mode is initiated, the relays 31, 32, and 34 are turned off, and the relays 35 and 36 are turned on. According to the grid charging mode, the rectifier 93, which is a diode full bridge, rectifies the single-phase grid voltage to charge the capacitor 92.

Capacitor 92 supplies DC power to oscillator 91, which is a full-bridge inverter called an H-bridge. Oscillator 91 supplies high-frequency current to coil 7 of transformer 13. The four MOSFETs of H-bridge 91 are PWM-controlled to control the waveform of the high-frequency current.

The transformer 13 has three coils 5, 7, and 8A wound around a soft magnetic core 13A. The coils 5, 7, and 8A are magnetically coupled by the soft magnetic core 13A. When the oscillator 91 supplies a high-frequency primary current to the coil 7, the battery-side converter 4A as a rectifier rectifies the secondary voltage induced in the coil 8A. The battery-side converter 4A also consists of a full-bridge inverter called an H-bridge. The voltage rectified by the battery-side converter 4A is applied to the battery 1 through relays 35 and 36. Ultimately, the grid charger 11 can charge the battery 1 using grid power.

The DCDC converter 12 consists of a battery-side converter 4B, a transformer 14, and a rectifier 61. The transformer 14 has coils 8B and 6 wound around a soft magnetic core 14A. The battery-side converter 4B, which consists of an oscillator, applies a high-frequency voltage to the coil 8B. The secondary voltage induced in the coil 6 is rectified by the rectifier 61 and then applied to the low-voltage battery 60.

The controller 30 has a battery heating mode in addition to the grid charging mode. This battery heating mode is implemented after the smoothing capacitor 2 is precharged. According to the battery heating mode, which is implemented when the temperature of the battery 1 is below a predetermined value, a high-frequency current circulating between the smoothing capacitor 2 and the battery 1 heats the battery 1.

This battery heating mode includes two modes. The first battery heating mode is called the battery-connected battery heating mode. The second battery heating mode is called the grid-connected battery heating mode.

First, the battery-connected battery heating mode will be described. Relays 35 and 36 are turned on, and battery 1 applies the battery voltage to battery-side converter 4A. Next, battery-side converter 4A, which is driven as an oscillator, supplies high-frequency current to coil 8A. This induces a high-frequency secondary voltage in coil 5, and the secondary current circulates in a closed loop circuit consisting of battery 1, coil 5, relay 31, smoothing capacitor 2, and relay 34.

As a result, the battery 1 is efficiently heated by the resistive loss. For example, it is assumed that the internal resistance of the battery 1 is 0.1 ohms and the effective value of the high-frequency current is 70 A. As a result, the battery 1 generates a resistive loss of approximately 490 W. This battery-connected battery heating mode can be implemented during periods when the propulsion motor is stopped and during periods when the propulsion motor is driven.

However, the battery heating power should be adjusted so that the sum of the high-frequency power for the battery heating mode and the power for driving the motor does not exceed a predetermined level. The battery heating power is controlled by PWM control of the H-bridge as the battery-side converter 4A. This battery heating mode is terminated when the temperature of the battery 1 reaches a predetermined value.

Next, the grid-connected battery heating mode is described. This grid-connected battery heating mode can be implemented simultaneously with the grid charging mode described above, or can be implemented alone. When the battery heating mode and the grid charging mode are implemented together, the battery heating power is suitably controlled so that the current of the battery 1 does not exceed a predetermined value. The oscillator 91 of the grid-side converter 9 is PWM controlled to control the battery heating power.

First, the sole implementation of the grid-connected battery heating mode is described. Relays 35 and 36 are turned off, and relays 31 and 34 are turned on. Grid power rectified by rectifier 93 is supplied to oscillator 91. Oscillator 91 applies a primary voltage to coil 7. As a result, a secondary voltage is induced in battery heating coil 5, and battery 1 and smoothing capacitor 2 are heated by high-frequency current.

Next, the case where the grid-tied battery heating mode and the grid charging mode are simultaneously implemented will be described. When the grid-tied battery heating mode is implemented, the relays 35 and 36 are turned on.
The grid power rectified by the rectifier 93 is charged in the capacitor 92. The oscillator 91, powered by the capacitor 92, supplies a high-frequency current to the coil 7. As a result, the high-frequency voltage induced in the battery heating coil 5 heats the battery 1. Furthermore, the secondary voltage induced in the coil 8A is rectified by the battery-side converter 4A, which serves as a rectifier. This charges the battery 1.

Figure 3 shows an example circuit of the battery-side converter 4A, the transformer 13, and the grid-side converter 9 shown in Figure 2. In Figure 3, a cross section of the transformer 13 is shown. Three coils 8A, 5, and 7 are wound around the central pole of the soft magnetic core 13A. The number of turns of the coil 5 is preferably one turn.

The effects of this embodiment will be explained. First, the transformer 13 of the grid charger 11 also serves as a transformer for the battery heating circuit that heats the battery 1. Furthermore, the battery side converter 4A and the grid side converter 9 of the grid charger 11 each also serve as an oscillator for this battery heating circuit. As a result, the low-temperature battery 1 can be heated by adding a simple circuit, and the weight and cost of the battery heating circuit can be reduced.

Next, the effect of the inductance of the battery heating coil 5 will be explained. First, when the relays 31 and 34 are turned off, the so-called contact arc problem of the relays 31 and 34 becomes serious. This problem is solved by applying a secondary reverse voltage to the coil 5 when the relays 31 and 34 are turned off. When the relays 31 and 34 are turned off, the battery side converter 4A applies a primary reverse voltage to the coil 8A. This induces a secondary reverse voltage in the coil 5. The direction of this secondary reverse voltage is opposite to the direction of the current flowing through the battery heating coil 5. This suppresses the adverse effect of the coil 5 when the relays 31 and 34 are turned off.

Furthermore, the technique of inducing a secondary reverse voltage in the battery heating coil 5 can be used to suppress the inrush current flowing through the smoothing capacitor 2 by turning on the precharge relay 32. First, by turning on relays 35 and 36, the battery-side converter 4A applies a primary reverse voltage to the coil 8A. This induces a secondary reverse voltage in the coil 5. The direction of this secondary reverse voltage is the direction that reduces the inrush current flowing through the smoothing capacitor 2. This reduces the inrush current.

A modified version of the transformer 13 and transformer 14 shown in FIG. 2 will be described with reference to FIG. 4. The soft magnetic core 13A of the transformer 15 shown in FIG. 4 has a first pole 101A, a second pole 101B, and a third pole 101C. The soft magnetic core 13A further has cross bars 101D, 101E, 101F, and 101G. Coils 5, 7, and 8A are wound around the first pole 101A, and coils 6 and 8B are wound around the third pole 101C. The second pole 101B has no coil.

Therefore, the magnetic flux of coils 5, 7, and 8A flows through a closed loop magnetic path formed by the first pole 101A, cross bar 101D, second pole 101B, and cross bar 101E. Similarly, the magnetic flux of coils 6 and 8B flows through a closed loop magnetic path formed by the third pole 101C, cross bar 101F, second pole 101B, and cross bar 101G.

In the end, the transformer 15 shown in FIG. 4 is equivalent to the two transformers 13 and 14 shown in FIG. 2. However, the soft magnetic core 15A of the transformer 15 is more compact than the soft magnetic cores 13A and 14A of the two transformers 13 and 14. In addition, the pole 101B shown in FIG. 4 can have a wall shape that surrounds the poles 101A and 101C. This can reduce electromagnetic noise.

Second Embodiment A second embodiment of the electric propulsion system of the present invention will be described with reference to Fig. 5. The electric propulsion system shown in Fig. 5 is similar to the electric propulsion system shown in Fig. 2. However, this embodiment uses one transformer 16 instead of the two transformers 13 and 14 shown in Fig. 2. Furthermore, this embodiment uses two coils 6A and 6B connected in series instead of the single coil 6 shown in Fig. 2.

This transformer 16 has six coils: 5, 7, 8A, 8B, 6A, and 6B. The battery-side converter 4A is connected to the coil 8A, and the battery-side converter 4B is connected to the coil 8B. The two coils 6A and 6B connected in series are connected to the rectifier 61.

The positive terminal B+ of the high-voltage battery 1 is connected to the positive terminal C+ of the smoothing capacitor 2 through a relay 31. The negative terminal B- of the battery 1 is connected to the negative terminal C- of the smoothing capacitor 2 through a relay 34 and a coil 5. A three-phase inverter 20 for driving the motor is connected in parallel with the smoothing capacitor 2. A relay 32 and a low resistance element 33 are connected in series with the relay 31 in parallel. The battery-side converters 4A and 4B are connected to the battery 1 through relays 35 and 36.

The coil 7 is connected to the electric grid through the grid-side converter 9. The grid-side converter 9 has an oscillator 91, a capacitor 92, and a rectifier 93 connected to the coil 7. The grid voltage is rectified by the rectifier 93. The rectified DC voltage charges the capacitor 92. The oscillator 91 converts the DC power of the capacitor 92 into high-frequency power and supplies it to the coil 7. In the end, the grid-side converter 9, the coil 7, the coils 8A and 8B, and the battery-side converters 4A and 4B form the grid charger already described.

Battery 1 charges low-voltage battery 6 through battery-side converters 4A and 4B, coils 8A and 8B, coils 6A and 6B, and rectifier 61. This operation is called DCDC converter mode. Battery-side converters 4A and 4B, coils 8A and 8B, coils 6A and 6B, and rectifier 61 form a DCDC converter for charging low-voltage battery 6. The secondary voltage induced in series-connected coils 6A and 6B is rectified by rectifier 61. Rectifier 61 charges low-voltage battery 60. Low-voltage battery 60, which has a rated voltage of 12V, supplies control power to controller 30.

Furthermore, coil 5, which is a battery heating coil, forms a closed loop circuit for battery heating together with battery 1 and smoothing capacitor 2. The secondary voltage induced in coil 5 circulates a high-frequency current in this closed loop circuit.

The operating modes implemented by the controller 30 are described. The controller 30 has a motor drive mode, a grid charging mode, a grid-connected battery heating mode, a battery-connected battery heating mode, and a DCDC converter mode. These modes are described in turn.

First, the grid charging mode will be described. First, relays 35 and 36 are turned on. When a rectifier 93 consisting of a diode bridge is connected to the 200 ACV electric grid, the rectifier 93 rectifies the grid voltage and charges a capacitor 92. An oscillator 91 connected to the capacitor 92 supplies a high-frequency current to the primary coil 7.

As a result, the secondary voltage induced in the secondary coil 8A is rectified by the battery-side converter 4A and applied to the battery 1. Similarly, the secondary voltage induced in the secondary coil 8B is rectified by the battery-side converter 4B and applied to the battery 1. The secondary coils 8A and 8B have the same number of turns. Ultimately, the battery-side converters 4A and 4B, acting as rectifiers, charge the battery 1 in parallel.

Next, the grid-connected battery heating mode will be described. This grid-connected battery heating mode is implemented when the temperature of the battery 1 is low and the rectifier 93 is connected to the electric grid. First, the relays 31 and 34 are turned on. The rectifier 93 rectifies the grid voltage and charges the capacitor 92. The oscillator 91 connected to the capacitor 92 supplies a high-frequency current, for example, 8 kHz, to the primary coil 7. The secondary voltage induced in the battery heating coil 5 causes a high-frequency current to flow in the closed loop circuit consisting of the coil 5, the battery 1, and the smoothing capacitor 2, and the battery 1 is heated. When the temperature of the battery 1 reaches a predetermined value, this grid-connected battery heating mode ends.

Next, the DCDC converter mode will be described. First, relays 35 and 36 are turned on. In this DCDC converter mode, the battery side converters 4A and 4B each operate as an oscillator. The battery side converter 4A supplies a high-frequency current to the coil 8A, and the battery side converter 4B supplies a high-frequency current to the coil 8B. The sum of the secondary voltages induced in the coils 6A and 6B is rectified by the rectifier 61 and applied to the low-voltage battery 60. The battery side converters 4A and 4B are PWM controlled according to the voltage of the low-voltage battery 60.

Next, the battery-connected battery heating mode will be described. The rectifier 93 is disconnected from the electric grid. First, the relays 31, 34, 35, and 36 are turned on. The battery-side converters 4A and 4B operating as oscillators supply high-frequency current to the coils 8A and 8B, and a secondary voltage is induced in the battery heating coil 5. As a result, the high-frequency current flows through a closed loop circuit consisting of the battery 1, the smoothing capacitor 2, and the coil 5, and the battery 1 is heated. Note that when the battery-connected battery heating mode and the motor drive mode are implemented simultaneously, the high-frequency current is limited so that the maximum current flowing through the battery 1 is less than a predetermined threshold value.

According to this embodiment, both the battery-connected battery heating mode and the DCDC converter mode use the battery-side converters 4A and 4B as oscillators. Thus, when the oscillators 4A and 4B supply primary current to the coils 8A and 8B, secondary voltages are induced in the coils 5, 6A, and 6B as secondary coils. In other words, the battery-connected battery heating mode and the DCDC converter mode are implemented simultaneously.

However, it is preferable that the battery-connected battery heating mode and the DCDC converter mode are each implemented independently. This problem is solved by employing a special transformer 16 called a flux-switching transformer.

Figures 6 and 7 are schematic cross-sectional views showing the structure of the transformer 16. The soft magnetic core 16A has three poles 101A, 101B, and 101C, and four cross bars 101D, 101E, 101F, and 101G. Pole 101A, cross bar 101D, pole 101B, and cross bar 101E form a first closed magnetic circuit. Pole 101C, cross bar 101F, pole 101B, and cross bar 101G form a second closed magnetic circuit.

In practice, these closed magnetic circuits have narrow air gaps to avoid magnetic saturation. Cross bars 101D and 101F magnetically short the upper ends of the three poles 101A, 101B, and 101C. Similarly, cross bars 101E and 101G magnetically short the lower ends of the three poles 101A, 101B, and 101C.

Coils 8A and 6A are wound around pole 101A, and coils 8B and 6B are wound around pole 101C. In other words, coils 8A and 6A are wound around the first closed magnetic circuit, and coils 8B and 6B are wound around the second closed magnetic circuit. However, coils 8A, 6A, 8B, and 6B are not wound around pole 101B, which is the common magnetic path of the first and second closed magnetic circuits.

The series-connected coils 6A and 6B have equal turns. The coils 8A and 8B have equal turns. The coils 5 and 7 are wound around the pole 101B. Preferably, the coil 5 has one turn. In the transformer 16, the magnetic coupling between the coils 8A and 8B and the coil 5 is called the flux sum coupling, and the magnetic coupling between the coils 8A and 8B and the coils 6A and 6B is called the flux difference coupling.

As shown in Figures 6 and 7, the battery-side converter 4A connected to the coil 8A consists of an H-bridge with two legs 401 and 402. Similarly, the battery-side converter 4B connected to the coil 8B consists of an H-bridge with two legs 403 and 404.

The controller 30, which has a flux sum mode and a flux difference mode, selects either flux sum coupling or flux difference coupling by switching the direction of the primary current supplied from the battery side converter 4B to the coil 8B. Implementing the flux sum mode selects flux sum coupling, and implementing the flux difference mode selects flux difference coupling. In both the flux sum mode and the flux difference mode, the first primary current supplied from the battery side converter 4A to the coil 8A has the same amplitude value and the same frequency value as the second primary current supplied from the battery side converter 4B to the coil 8B.

Figure 6 shows the flow of current and magnetic flux in the flux sum mode. In this flux sum mode, the first primary current supplied to coil 8A has the same phase as the second primary current supplied to coil 8B. In other words, the first primary current and the second primary current have the same waveform. As a result, the magnetic flux F1 formed by coil 8A in pole 101A flows upward, and the magnetic flux F2 formed by coil 8B in pole 101C also flows upward. Therefore, the two magnetic fluxes F1 and F2, which have the same waveform, flow downward in pole 101B.

According to this flux sum mode, secondary voltages are induced in coil 5 and coil 7. Since coil 7 is connected to oscillator 91, the effect of the secondary voltage induced in coil 7 is ignored. The secondary voltage induced in coil 5 implements the battery heating mode. That is, this flux sum mode is employed in the battery-connected battery heating mode.

Furthermore, according to this flux sum mode, secondary voltages are induced in coils 6A and 6B. However, coils 6A and 6B are connected to each other so that the sum of the secondary voltages of the series-connected coils 6A and 6B is zero. In other words, the secondary voltage applied to the rectifier 61 by coil 6A is opposite to the secondary voltage applied to the rectifier 61 by coil 6B. As a result, the sum of the secondary voltages applied to the rectifier 61 by coils 6A and 6B is zero, and the DCDC converter mode is not implemented in the flux sum mode.

Figure 7 shows the current and flux flow in flux difference mode. In this flux difference mode, the first primary current supplied to coil 8A has the opposite phase compared to the second primary current supplied to coil 8B. In other words, the first primary current and the second primary current have opposite waveforms. The change from flux sum mode to flux difference mode is performed by inverting the waveform of the second primary current. This change is easily performed by PWM control of the H-bridge 4B, which is the battery side converter.

In the magnetic flux difference mode, leg 403 shown in FIG. 7 has the same switching pattern as leg 404 shown in FIG. 6, and leg 404 shown in FIG. 7 has the same switching pattern as leg 403 shown in FIG. 6. As a result, the primary current supplied to coil 7B by H-bridge 4B shown in FIG. 7 has an inverse waveform to the primary current supplied to coil 7B by H-bridge 4B shown in FIG. 6.

In the flux difference mode shown in FIG. 7, a first primary current supplied to coil 8A forms a magnetic flux F1 in pole 101A, and a second primary current supplied to coil 8B forms a magnetic flux F2 in pole 101C. Magnetic flux F1 and magnetic flux F2 have the same waveform. However, magnetic flux F1 flows upward through pole 101A, while magnetic flux F2 flows downward through pole 101C.

In conclusion, according to this magnetic flux difference mode, magnetic fluxes F1 and F2 having the same waveform flow in opposite directions in pole 101B. This means that the sum of the magnetic fluxes flowing in pole 101B is zero. Therefore, the secondary voltages induced in coils 5 and 7 are zero, respectively, and the battery heating mode is not implemented.

Next, in this magnetic flux difference mode, magnetic flux F1 and magnetic flux F2 having the same direction flow through poles 101A and 101C. As a result, the sum of magnetic flux F1 and magnetic flux F2 induces secondary voltages in coils 6A and 6B, respectively. As a result, coils 6A and 6B apply secondary voltages of the same direction to rectifier 61. Rectifier 61 rectifies the sum of the secondary voltages of the two coils 6A and 6B and applies it to low-voltage battery 60. Ultimately, this magnetic flux difference mode is adopted in a DCDC converter mode that transmits DC power from battery 1 to battery 60.

This DCDC converter mode can be implemented simultaneously with the motor driving mode. With this DCDC converter mode, during the period when the low-voltage battery 60 is charged through the coils 6A and 6B, the sum of the secondary voltage of the coil 5 induced by the coil 6A and the secondary voltage of the coil 5 induced by the coil 6B becomes zero. Therefore, in the motor driving mode, the voltage of the smoothing capacitor 2 is prevented from fluctuating due to the secondary voltage of the coil 5. The battery-side converters 4A and 4B are PWM controlled so that the discharge current flowing through the battery 1 does not exceed a predetermined maximum threshold.

The flow of magnetic flux in the grid charging mode described above will now be explained. The oscillator 91 supplies primary power to the coil 7. The coil 7 forms a magnetic flux sum coupling with the coils 8A and 8B. Therefore, as shown in FIG. 6, the coil 7 wound around the pole 101B passes magnetic flux F1 through the pole 101A and magnetic flux F2 through the pole 101C. In other words, half of the magnetic flux formed by the coil 7 flows through the pole 101A, and the other half flows through the pole 101C. Ultimately, the rectifiers 4A and 4B charge the battery 1 in parallel. In this grid charging mode, the sum of the secondary voltages of the series-connected coils 6A and 6B is zero. Therefore, the DCDC converter mode is not implemented.

Third embodiment A third embodiment of the electric propulsion system of the present invention will be described with reference to Fig. 5. However, in this third embodiment, the coil 5 is omitted. The controller 30 has the grid charging mode and the DCDC converter mode already described. The grid charging mode is performed by the flux sum mode shown in Fig. 6, and the DCDC converter mode is performed by the flux difference mode shown in Fig. 7.

In the end, the battery circuit associated with the electric propulsion system shown in FIG. 5 can independently implement the grid charging mode and the DCDC converter mode by adopting the soft magnetic core 16A shown in FIG. 6 and FIG. 7. This makes it possible to avoid overcharging the low-voltage battery 60 in the grid charging mode.

Fourth embodiment A fourth embodiment of the electric propulsion system of the present invention will be described with reference to Fig. 5. However, in this fourth embodiment, the coil 7 is omitted. The controller 30 has the battery heating mode and the DCDC converter mode already described. The battery heating mode is performed by the flux sum mode shown in Fig. 6, and the DCDC converter mode is performed by the flux difference mode shown in Fig. 7.

In the end, the battery circuit attached to the electric propulsion system shown in FIG. 5 can independently implement the battery heating mode and the DCDC converter mode by adopting the soft magnetic core 16A shown in FIG. 6 and FIG. 7. According to this embodiment, the low-temperature battery 1 can be heated by AC simply by adding a battery heating coil 5 to the transformer of the step-down DCDC converter that charges the low-voltage battery 60 with the high-voltage battery 1.

In a modified embodiment of each of the embodiments described above, the battery side converter 4 or the battery side converters 4A and 4B can be connected to the high voltage battery 1 through the system relays 31 and 34. This allows the safety relays 35 and 36 to be omitted. Furthermore, the grid charger 11 may be a bidirectional charger with a transformer.

Claims (11)

1. An electric propulsion system comprising: a high-voltage battery that supplies motor drive power to a motor drive circuit for driving a propulsion motor; a transformer electrically connected to the high-voltage battery; and a controller that controls a current supplied to a coil of the transformer,
1. An electric propulsion system, comprising: a transformer having three or more coils wound around a common soft magnetic core. The electric propulsion system according to claim 1, wherein the controller has a battery heating mode in which a secondary current flows through the high voltage battery by inducing a secondary voltage in a battery heating coil consisting of one of the three or more coils. the transformer is part of a grid charger that charges the high-voltage battery with power from a power grid;
the grid charger includes a grid-side converter that connects one of the coils and the power grid, and a battery-side converter that connects the other of the coils and the high-voltage battery,
3. The electric propulsion system according to claim 2, wherein the other coil comprises a battery heating coil that heats the high-voltage battery by supplying high-frequency power to the high-voltage battery. The electric propulsion system according to claim 3, wherein the battery heating coil, together with the high-voltage battery and a predetermined power storage device, forms a closed loop circuit in which the secondary current circulates. The electric propulsion system according to claim 4, wherein the predetermined power storage device is a smoothing capacitor connected to a pair of input terminals of the motor drive circuit. The electric propulsion system according to claim 1, wherein the controller executes at least two of a grid charging mode in which the high-voltage battery is charged through the transformer by using power from an electric grid, a DC-DC converter mode in which the low-voltage battery is charged through the transformer by using power from the high-voltage battery, and a battery heating mode in which a battery heating current is supplied to the high-voltage battery through the transformer. The electric propulsion system according to claim 6, wherein the controller executes all of the grid charging mode, the DC-DC converter mode, and the battery heating mode. The soft magnetic core (16) has a first magnetic path (101A), a second magnetic path (101C), and a third magnetic path (101B),
the first magnetic path, the second magnetic path, and the third magnetic path are magnetically connected in parallel;
A first coil (8A) and a second coil (6A) are wound around the first magnetic path,
A third coil (8B) and a fourth coil (6B) are wound around the second magnetic path,
A fifth coil (5 and/or 7) is wound around the third magnetic path,
2. The electric propulsion system according to claim 1, wherein the second coil (6A) and the fourth coil (6B) are connected in series. The electric propulsion system according to claim 8, wherein the controller (30) selectively utilizes either the total secondary voltage of the second coil (6A) and the fourth coil (6B) or the secondary voltage of the fifth coil (5 and/or 7) by controlling the primary current supplied to the first coil (8A) and the third coil (8B) as primary coils. 1. An electric propulsion system comprising: a high-voltage battery that supplies motor drive power to a motor drive circuit for driving a propulsion motor; a transformer electrically connected to the high-voltage battery; and a controller that controls a current supplied to a coil of the transformer,
the transformer has a smoothing capacitor connected to a pair of input terminals of the motor drive circuit and a battery heating coil forming a closed loop circuit together with the high voltage battery;
The controller:
1. An electric propulsion system comprising: a battery heating mode for inducing a secondary voltage in the battery heating coil to circulate a secondary current in the closed loop circuit when the temperature of the high voltage battery is below a predetermined value. the closed loop circuit further includes a relay connecting the high voltage battery and the smoothing capacitor;
The electric propulsion system of claim 10 , wherein the controller induces a voltage in the battery heating coil to reduce a current through the relay when the relay is open.

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