JP7168475B2 - power conversion circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power conversion circuit for charging a main battery and an auxiliary battery with external AC power.

In a PHV (plug-in hybrid vehicle), an EV (electric vehicle), or the like, an on-vehicle battery can be charged using power from an external AC power supply (for example, a power system from an electric power company).

In Patent Document 1, in power conversion between the system and the main battery and the auxiliary battery using a three-port transformer, DC voltage is applied to suppress efficiency deterioration due to battery SOC (state of charge) fluctuations. Varying according to the battery SOC is shown.

Further, in Patent Document 2, a transformer that exchanges power between the system and the main battery and a transformer that exchanges power between the main battery and the auxiliary battery are provided, and the phase difference between both sides of each transformer is controlled. Controlling power exchange is shown.

JP 2015-119598 A JP 2018-14794 A

Here, the main battery usually has a higher voltage and a larger capacity than the auxiliary battery, and the charging power from the system is also large. Therefore, in the power exchange in the transformer, the phase difference between the system side bridge circuit and the main battery side bridge circuit is set larger than the phase difference between the system side bridge circuit and the auxiliary battery side bridge circuit. Therefore, when charging the main battery and the auxiliary battery at the same time, the power from the system side bridge circuit is transferred via the auxiliary battery side bridge circuit based on the phase difference between the main battery side bridge circuit and the auxiliary battery side bridge circuit. The power supplied to the main battery side bridge circuit is detoured, and the loss due to the auxiliary battery side bridge circuit is increased.

A power conversion circuit according to the present invention has two arms composed of two switching elements connected in series, a system side bridge circuit that outputs AC power with AC power from the outside as an input source, and a first port. It has a 3-port transformer to which a grid-side bridge circuit is connected and two arms consisting of two switching elements connected in series, and is connected to the second port of the 3-port transformer and supplies charging power to the main battery A main machine side bridge circuit, and an auxiliary machine side bridge circuit that has two arms consisting of two switching elements connected in series, is connected to the third port of the 3-port transformer, and supplies charging power to the auxiliary machine battery. , to increase the inductance in the auxiliary equipment side bridge circuit, and the necessary phase difference of the AC in the auxiliary equipment side bridge circuit with respect to the AC in the system side bridge circuit required for charging the auxiliary equipment battery, to charge the main equipment battery The required phase difference for the AC in the main machine side bridge circuit with respect to the AC in the system side bridge circuit is brought close to the required phase difference.

In addition, by increasing the inductance in the auxiliary equipment side bridge circuit, the required phase difference of the AC in the auxiliary equipment side bridge circuit with respect to the AC in the system side bridge circuit is adjusted to the required phase difference of the AC in the main equipment side bridge circuit with respect to the AC in the system side bridge circuit. should be equal to

Further, it is preferable to increase the inductance in the accessory-side bridge circuit by providing an additional inductor or increasing the leakage inductance at the third port in the accessory-side bridge circuit.

In addition, the power conversion circuit is mounted on the vehicle, and is provided between the grid side bridge circuit and the first port of the 3-port transformer, and has a relay that controls connection or disconnection between the two. The bridge circuit and the 1st port of the 3-port transformer are separated, power is transmitted between the bridge circuit on the main side and the bridge circuit on the auxiliary side, and when the vehicle is stopped, the grid-side bridge circuit and the 1st port of the 3-port transformer are relayed. and transmit power from the system side bridge circuit to the main side bridge circuit and the auxiliary side bridge circuit.

According to the present invention, power loss during simultaneous charging of the main battery and the auxiliary battery can be reduced.

It is a figure which shows the structure of the system using the power inverter circuit which concerns on embodiment. FIG. 2 is a diagram for explaining circuit operation when the vehicle is stopped and when the vehicle is running, (a) when the vehicle is stopped and (b) when the vehicle is running. FIG. 3 is a diagram showing an equivalent circuit of a 3-port transformer, where (a) is an equivalent circuit of an ideal 3-port transformer with a coupling ratio of 1, and (b) is a Y-connected transformer equivalent circuit. It is a figure which shows the 3 port transformer equivalent circuit after Ydelta conversion. FIG. 4 is a diagram showing a waveform of a current iy in a transformer winding LL3 when power detouring occurs at a certain duty value and a calculation result of the current effective value iyrms by a circuit simulator; FIG. 10 is a diagram showing current waveforms of transformer windings LL2 and LL3 when the accessory-side inductance _L3r is set so that φ ₁ =φ ₂ during charging while the vehicle is stopped; It is a figure which shows the operation|movement waveform by the rated 100A output during driving|running|working, (a) shows a main battery side, (b) shows an auxiliary battery side.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described based on the drawings. It should be noted that the invention is not limited to the embodiments described herein.

FIG. 1 is a diagram showing the configuration of a system using a power conversion circuit according to one embodiment.

First, the system side bridge circuit A having a power factor improving function connected to the first transformer winding LL1 of the 3-port transformer TR via the first port will be described.

For example, a capacitor C0 is connected in parallel to an external AC power supply 10 such as a 100 V AC commercial power supply, and one end of the external AC power supply 10 is connected to two diodes D1 and D2 facing the same direction forming a rectifier circuit in series. Connected to the midpoint of the connection. The external AC power supply 10 is supplied from an electric power company and is appropriately called engagement. In addition, the anode side of the series connection of the diodes D1 and D2 is the positive side bus line, the cathode side is the negative side bus line, and the negative side bus line is connected to the ground. A smoothing capacitor C1 is connected between the positive and negative bus lines, and a full bridge BR1 including an arm composed of series-connected switching elements S1 and S2 and an arm composed of series-connected switching elements S3 and S4 is connected. It is

The middle point of the switching elements S1 and S2 and the middle point of the switching elements S3 and S4 are connected to the first port, which is both ends of the first transformer winding LL1 of the 3-port transformer TR, via the relay RL. Also, the intermediate port of the first transformer winding LL1 is connected to the other end of the external AC power supply 10 .

Therefore, the AC component from the external AC power supply 10 is applied between the midpoint of the diodes D1 and D2 and the intermediate port of the first transformer winding LL1 of the 3-port transformer TR. DC voltage VC1 rectified by rectifier diodes D1 and D2 and smoothed by smoothing capacitor _C1 is applied between the positive and negative bus lines, and is applied to first transformer winding LL1 of transformer TR by switching of switching elements S1 to S4. A predetermined AC voltage V _uv is applied. Here, by controlling the switching of the full bridge BR1 composed of the switching elements S1 to S4 in accordance with the output (system voltage) of the external AC power supply that fluctuates at the line cycle (eg, 50 Hz), the first transformer winding LL1 The phase of the voltage current in can be controlled to reduce losses.

A main side bridge circuit B is connected to the second port, which is both ends of the second transformer winding LL2 of the 3-port transformer TR, and an auxiliary side bridge circuit is connected to the third port, which is both ends of the third transformer winding LL3. Circuit C is connected. Thus, the system side bridge circuit A, the main side bridge circuit B, and the auxiliary side bridge circuit C share the transformer core.

The main machine side bridge circuit B has a full bridge BR2 including an arm formed by a series connection of switching elements S5 and S6 and an arm formed by a series connection of switching elements S7 and S8. , the middle point of the switching elements S7 and S8 is connected to the second port of the 3-port transformer TR, that is, to both ends of the second transformer winding LL2. A smoothing capacitor C2 and a main battery 12 are connected in parallel to the full bridge BR2. Therefore, by controlling the switching of the switching elements S5 to S8, the applied voltage _Vwx to the second port of the three-port transformer can be controlled, and the voltage of the transformer winding LL2 can be controlled.

The accessory-side bridge circuit C has the same configuration as the above-described main-side bridge circuit B, and has an arm composed of series-connected switching elements S9 and S10 and an arm composed of series-connected switching elements S11 and S12. The middle point of the switching elements S9 and S10 and the middle point of the switching elements S11 and S12 are connected to the third port of the 3-port transformer TR, that is, both ends of the transformer winding LL3. there is A smoothing capacitor C3 and an auxiliary battery 14 are connected in parallel to the full bridge BR3. Therefore, by controlling the switching of the switching elements S9 to S12, the applied voltage _Vyz to the third port of the three-port transformer can be controlled, and the voltage of the transformer winding LL3 can be controlled.

A backflow prevention diode is connected in parallel to each of the switching elements S1 to S12.

Here, the voltage ratio between the ports can be determined by the ratio of the winding numbers of the transformer windings LL1, LL2, and LL3 of the 3-port transformer TR. Further, by controlling the phase difference of the system side bridge circuit A: the main machine side bridge circuit B: the auxiliary machine side bridge circuit C, the amount of power transmission can be controlled. That is, the amount of power transmitted between circuits is proportional to the phase difference between the circuits and inversely proportional to the inductance between the circuits. The phase may be the phase of the switching cycle in the bridge circuit, for example.

In the system side bridge circuit A, the main side bridge circuit B, and the auxiliary side bridge circuit C, the switching elements in the full bridges BR1, BR2, and BR3 are PWM (pulse width modulation) controlled to control the waveform to the corresponding port. do. In particular, the grid-side bridge circuit A has a power factor correction (PFC) function, and by modulating the duty ratio, suppresses input current harmonics and controls the 3-port transformer TR at a predetermined phase. supply power to the primary side of the In addition, in the main machine side bridge circuit B and the auxiliary machine side bridge circuit C, the switching of the full bridges BR2 and BR3 is controlled to control the phase difference with the system side bridge circuit A, and the inductance between each circuit is appropriately adjusted. By setting, the amount of power transmitted between each circuit is controlled.

"System Behavior"
2A and 2B are diagrams for explaining the circuit operation when the vehicle is stopped and when the vehicle is running. FIG. 2A shows the operation when the vehicle is stopped, and FIG. 2, the circuit of FIG. 1 is shown in a simplified form.

FIG. 2(a) shows the state when the vehicle is stopped, the relay RL is turned on, and charging (for example, about 3000 W) from the external AC power supply 10 to the main battery 12 is performed. Also, even during charging while the vehicle is stopped, a plurality of auxiliary equipment system components such as the battery monitoring unit operate. Therefore, small electric power of about several hundred W is supplied to the auxiliary battery 14 via the 3-port transformer TR so that the auxiliary battery 14 is not exhausted.

FIG. 2(b) shows the state during running, in which the relay RL is turned off and the system side bridge circuit A is disconnected from the first port. In this state, power is supplied from the main battery 12 to the auxiliary battery 14 as required. At this time, since the PFC function is unnecessary, the duty value is a fixed value, for example, duty=50% at which the conversion efficiency is maximized. In this way, by switching the on/off state of the relay RL and the circuit operation for each operation scene, it is possible to integrate the functions of in-vehicle charging and DC/DC conversion.

Except for the fact that the duty varies with the line period during charging while the vehicle is stopped as shown in FIG.

FIG. 3 is a diagram showing an equivalent circuit of the 3-port transformer TR, where (a) is an equivalent circuit of an ideal 3-port transformer with a coupling ratio of 1, and (b) is a Y-connected transformer equivalent circuit.

n _tr1 , n _tr2 , and n _tr3 in FIG. 3A are the number of turns of transformer windings LL1, LL2, and LL3 to which the system side bridge circuit A, the main side bridge circuit B, and the auxiliary side bridge circuit C are connected, respectively. where _Lm is the excitation inductance, and L1, L2 _, and L3 _are the inductance values externally attached to _each winding. At this time, if the turns ratio is N ₁₂ =n _tr1 /n _tr2 , N ₁₃ =n _tr1 /n _tr3 , and V _wx ′=N ₁₂ ·V _wx , V _yz ′=N ₁₃ ·V _yz , three full A Y-connected transformer equivalent circuit using the bridges BR1, BR2, and BR3 as pulse voltage sources can be rewritten as shown in FIG. 3(b).

In order to derive the transmission power between the full bridges BR1, BR2 and BR3, it is necessary to convert the Y-connection equivalent circuit of FIG. 3(b) into a Δ-connection equivalent circuit.

FIG. 4 is a diagram showing a three-port transformer equivalent circuit after YΔ conversion. At this time, the inductance values _L12r , _L13r and _L23r between the pulse voltage sources are given by _L12r = _{Lk/L3r , L13r} = _Lk / _L2r and _L23r = _Lk / _L1r , respectively. . Here, L _k is a denominator term that appears during Y-Δ conversion and is given by L _k =L _1r ·L _2r +L _1r ·L _3r +L _2r ·L _3r .

_In the delta-connection equivalent circuit shown _in FIG. Assuming that the transmission power to the machine battery ₁₄ is P23, _P12 , _P13 , and _P23 are given by the relationship of Equation (1).

Here, δ (=2πduty) is the duty ratio of the full bridges BR1, BR2, and BR3, and in this embodiment, δ is synchronized in all bridge circuits during charging while the vehicle is stopped. V _uv (upper bar), V _wx (upper bar), and V _yz (upper bar) are the amplitudes of each pulse voltage source. From equation (1), under the operating conditions of φ ₁ >φ ₂ , P ₁₂ and P ₁₃ are positive, and power is transmitted from system side bridge circuit A to main side bridge circuit B and auxiliary side bridge circuit C. be. Here, _P23 is negative, and power is transmitted from the accessory side bridge circuit C to the main side bridge circuit B. This is because power greater than or equal to the power required by the load of the auxiliary battery 14 is transmitted from the grid-side bridge circuit A to the auxiliary-side bridge circuit C, and the remaining power bypasses the auxiliary-side bridge circuit C to It shows that it is transmitted to the side bridge circuit B.

FIG. 5 is a diagram showing the waveform of the current _{iy in the transformer winding LL3 when power bypass occurs at a certain duty value and the calculation result of the current effective value iyrms by} the circuit simulator. Here, the accessory load is 16A. Thus, while the required current of the accessory load is 16 A, the effective value i _yrms of the current of the transformer winding LL3 is 30 A, and the bypass power increases the current stress in the accessory side bridge circuit C. I understand.

On the auxiliary equipment side bridge circuit C side, where the voltage is low, the current effective value increases significantly with the bypass power of several hundred watts. It is necessary to suppress detour power.

From the above equation ( ₁ ), in order to suppress the power P23 bypassing the auxiliary equipment side bridge circuit C to zero, the _phase differences φ1 and φ2 must be equal, or the _phase difference _φ2 must be larger _than φ1. do it. On the other hand, the phase differences φ ₁ and φ ₂ must be increased in proportion to the charging power of the main battery 12 and the auxiliary battery 14, respectively. The phase difference φ1 between _B is necessarily larger _than φ2.

On the other hand, by increasing the accessory-side inductance _L3r in _FIG . The power detoured to the bridge circuit B on the main side can be suppressed. When power is transmitted to the auxiliary device side bridge circuit C by detouring the main device side bridge circuit B, the detour power amount is small compared to the transmission amount of the main device side bridge circuit B and causes almost no problem.

FIG. 6 is a diagram showing current waveforms of the transformer windings LL2 and LL3 when the accessory-side inductance _L3r is set so that _{φ1 =} φ2 during charging while the vehicle is stopped. The current effective value i _yrms is equivalent to the load current of 16 A, and it can be seen that the detour power to the accessory-side bridge circuit can be suppressed.

At this time, if V _uv (upper bar)=V _wx (upper bar)=V _yz (upper bar) in equation (1), the inductance value L _3r required for bypass power suppression is given by the following equation. The means for obtaining the required inductance _L3r can be implemented by adding a fixed inductor to the transformer winding LL3 to which the accessory-side bridge circuit C of the 3-port transformer TR is connected, or by adjusting the leakage L component through transformer structural design. is. An additional fixed inductor LL3+ is shown in dashed lines in FIG.

FIG. 7 is a diagram showing operating waveforms at a rated 100A output during running (FIG. 2(b)) under the inductance design conditions given by equation (2), (a) being the main battery side, ( b) shows the auxiliary battery side. During running, there is no need to improve the power factor, and by operating with δ in Equation (1) fixed at 0.5, the power that can be transmitted can be increased. In addition, in circuit conditions where the inductance L _23r between the main side bridge circuit B and the auxiliary side bridge circuit C in the Δ connection is increased by increasing the inductance L _3r of the auxiliary side bridge circuit C for detour suppression It is also possible to transmit the electric power necessary for running. That is, as shown in FIG. 2(b), the auxiliary battery 14 can be charged at 100A.

"Effect of embodiment"
According to this embodiment, the relay RL is provided to disconnect the system side bridge circuit A from the 3-port transformer TR during running. Therefore, the 3-port transformer TR, the main machine side bridge circuit B, and the auxiliary machine side bridge circuit C can be used as a DC/DC converter between the main machine battery 12 and the auxiliary machine battery 14, and efficient power transmission can be performed. .

Further, when charging from the external AC power supply 10 while the vehicle is stopped, power transmission by phase difference modulation is performed in the system side bridge circuit A, the main side bridge circuit B, and the auxiliary side bridge circuit C connected to the 3-port transformer TR. can be done. Here, when performing power transmission by such phase difference modulation, depending on the load state of the system-side bridge circuit A, the main-side bridge circuit B, and the auxiliary-side bridge circuit C, power bypass occurs. In particular, when simultaneously charging a load (battery) with a large voltage difference, such as the main battery 12 and the auxiliary battery 14, power is transferred to the main battery bridge circuit B bypassing the auxiliary bridge circuit C with the lower voltage. If this occurs, the current stress on the windings and semiconductor switches is large, and there is concern that the efficiency will deteriorate. In the present embodiment, during simultaneous charging, the required phase difference between the system side bridge circuit A and the main side bridge circuit B and the required phase difference between the system side bridge circuit A and the accessory side bridge circuit C are made equal. , Grid: By setting the equivalent inductance value between the accessory side bridge circuits, the detour power can be suppressed. At this time, the equivalent inductance value between the system side bridge circuit A and the accessory side bridge circuit C can be adjusted by the inductance value on the transformer winding LL3 connected to the accessory side bridge circuit C.

Also, the amount of power transmitted between circuits is proportional to the phase difference between the circuits and inversely proportional to the equivalent inductance value between the circuits. During charging while the vehicle is stationary, most of the charging period is during operation with constant power (steady period). Therefore, if the equivalent inductance value between circuits is designed in advance to prevent power detours during the steady period, detour power can be suppressed. Thus, the required phase difference between the system side bridge circuit A and the main machine side bridge circuit B and the required phase difference between the system side bridge circuit A and the auxiliary machine side bridge circuit C can be made equal.

In this way, by designing the inductance values to keep the required phase difference in the steady period of simultaneous charging equal, it is possible to suppress the detour power, which is a factor of deterioration in efficiency.

10 external AC power supply, 12 main machine battery, 14 auxiliary machine battery, A system side bridge circuit, B main machine side bridge circuit, C auxiliary machine side bridge circuit, BR1, BR2, BR3 full bridge, C0 to C3 capacitor, D1, D2 diode , LL1, LL2, LL3 transformer windings, RL relays, S1 to S12 switching elements, TR 3-port transformer.

Claims (4)

A grid-side bridge circuit that has two arms composed of two switching elements connected in series and that outputs AC power from an input source of AC power from the outside;
a 3-port transformer in which a grid-side bridge circuit is connected to a first port;
a main machine side bridge circuit having two arms consisting of two switching elements connected in series, connected to the second port of the 3-port transformer and supplying charging power to the main machine battery;
an auxiliary equipment-side bridge circuit having two arms composed of two switching elements connected in series, connected to a third port of a three-port transformer, and supplying charging power to an auxiliary battery;
including
By increasing the inductance in the auxiliary equipment side bridge circuit, the necessary phase difference of the AC in the auxiliary equipment side bridge circuit with respect to the AC in the system side bridge circuit required for charging the auxiliary equipment battery is adjusted to the required phase difference for charging the main equipment battery. Close to the required phase difference for the AC in the main machine side bridge circuit with respect to the AC in the system side bridge circuit,
power conversion circuit. In the power conversion circuit according to claim 1,
Increase the inductance in the auxiliary equipment side bridge circuit so that the required phase difference of the AC in the auxiliary equipment side bridge circuit with respect to the AC in the grid side bridge circuit is equal to the required phase difference for the AC in the main equipment side bridge circuit with respect to the AC in the grid side bridge circuit. to make
power conversion circuit. In the power conversion circuit according to claim 1 or 2,
increasing the inductance in the accessory-side bridge circuit by providing an additional inductor or increasing the leakage inductance at the third port in the accessory-side bridge circuit;
power conversion circuit. The power conversion circuit according to any one of claims 1 to 3,
The power conversion circuit is installed in the vehicle,
A relay provided between the system side bridge circuit and the first port of the 3-port transformer and controlling connection or disconnection between the two,
When running, the system side bridge circuit and the first port of the 3-port transformer are separated by a relay, power is transmitted between the main side bridge circuit and the auxiliary side bridge circuit,
When the vehicle is stopped, the grid side bridge circuit and the first port of the 3-port transformer are connected by a relay, and power is transmitted from the grid side bridge circuit to the main machine side bridge circuit and the auxiliary machine side bridge circuit.
power conversion circuit.

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