DC power conversion device and control method

Abstract

A first bridge circuit in a DC power conversion device according to an embodiment is driven by a first drive signal, and converts first DC power into first AC power. The second bridge circuit is driven by a second drive signal and converts second DC power of a second DC voltage into second AC power. The inductance element is disposed between the first bridge circuit and the second bridge circuit. The control device determines a phase difference between the first drive signal and the second drive signal used in DAB phase shift control, generates the first drive signal and the second drive signal according to the phase difference, and drives the first bridge circuit and the second bridge circuit. The control device determines an allowable range of a phase difference using the first DC voltage and the second DC voltage, and generates the first drive signal and the second drive signal that limit the phase difference within the allowable range when limiting the magnitude of the current flowing through the inductance element.

Description

Technical Field

[0001] Embodiments of the present invention relate to a DC power conversion device and a control method. Background Art

[0002] One control method for a DC power converter is the DAB (Dual Active Bridge) method. A DAB DC power converter includes a main circuit in which the AC sides of a pair of full-bridge circuits (DC / AC converter circuits) are connected to each other via an inductor element such as a transformer.

[0003] In DAB power conversion control, the direction of power transmission and the amount of power conversion can be controlled by adjusting the phase relationship between the drive signals for the primary-side full-bridge circuit and the secondary-side full-bridge circuit. If voltage fluctuations occur between the input and output voltages of a DC power converter, the current that causes power conversion may not flow as expected.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Re-Publication No. 2019 / 167271 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] An object of the present invention is to provide a DC power conversion device and a control method capable of reducing the influence of voltage fluctuations occurring between the input voltage and the output voltage of a DAB type DC power conversion device.

[0009] Means for solving problems

[0010] A DC power converter according to an embodiment performs power conversion between first and second DC powers using a DAB method for transferring power between the first and second DC powers. The DC power converter includes a first bridge circuit, a second bridge circuit, an inductor element, and a control device. The first bridge circuit is driven by a first drive signal to convert the first DC power into first AC power and output it to a first AC terminal. The second bridge circuit is driven by a second drive signal to convert the second DC power having a second DC voltage into second AC power and output it to a second AC terminal. The inductor element is disposed between the first and second bridge circuits and connected to the first and second AC terminals, respectively. The control device determines the phase difference between the first and second drive signals used in phase shift control using the DAB method, generates the first and second drive signals for driving the first and second bridge circuits based on the phase difference, and drives the first and second bridge circuits using the first and second drive signals. The control device generates the first drive signal and the second drive signal that limit the phase difference to the allowable range by using the first DC voltage and the second DC voltage to determine the allowable range of the phase difference and limit the magnitude of the current flowing in the inductor element. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a configuration diagram of a power conversion device according to an embodiment.

[0012] Figure 2 A diagram showing an equivalent circuit of an inductor element.

[0013] Figure 3 This is a diagram for explaining the operation of the DC / DC converter.

[0014] Figure 4A This is a block diagram of a control device for a power conversion device according to an embodiment.

[0015] Figure 4B This is a diagram for explaining a calculation formula used by the control device according to the embodiment.

[0016] Figure 5 This is a diagram for explaining a current waveform generated by control according to the embodiment.

[0017] Figure 6 This is a diagram for explaining an example of a current waveform. DETAILED DESCRIPTION

[0018] The following describes a DC power conversion device and control method according to an embodiment with reference to the accompanying drawings. In the following description, components having the same or similar functions are denoted by the same reference numerals. Furthermore, repeated descriptions of these components may be omitted. Furthermore, electrical connection may be simply referred to as "connection." The following description of "equal in size" also includes the case of being substantially equal.

[0019] (Implementation Method)

[0020] Figure 1 It is a configuration diagram of a DC power conversion device 100 according to the embodiment.

[0021] The DC power conversion device 100 includes a DC / DC converter 102 forming a main circuit and a control device 103 .

[0022] The DC power conversion device 100 further includes voltage detectors 171 and 172 and a current detector 141 for detecting the operating state of the main circuit.

[0023] The DC power conversion device 100 includes primary-side DC terminals 102 a and 102 b and secondary-side DC terminals 102 c and 102 d as terminals for connection to an external bus or the like.

[0024] The DC / DC converter 102 performs power conversion (DC / DC conversion) between a primary-side DC voltage Vdc1 between primary DC terminals 102 a and 102 b and a secondary-side DC voltage Vdc2 between secondary-side DC terminals 102 c and 102 d .

[0025] DC / DC converter 102 is a DAB-configured DC / DC converter. For example, DC / DC converter 102 includes a primary-side bridge circuit 110, a secondary-side bridge circuit 120, an inductor 130, and smoothing capacitors 150 and 160. Primary-side bridge circuit 110 and secondary-side bridge circuit 120 are examples of a pair of bridge circuits.

[0026] The primary-side bridge circuit 110 forms a single-phase full-bridge circuit. Specifically, the primary-side bridge circuit 110 includes semiconductor switching elements SW1 to SW4 connected between a high-potential power supply line PL1 and a low-potential power supply line NL1. Power supply lines PL1 and NL1 are connected to primary-side DC terminals 102a and 102b, respectively. A smoothing capacitor 150 is connected between power supply lines PL1 and NL1 to stabilize the primary-side DC voltage Vdc1.

[0027] Semiconductor switching elements SW1 and SW2 are connected in series via node N1a, forming a first arm 111 connected between power supply line PL1 and power supply line NL1. Node N1a is connected to AC terminal 123a. Similarly, semiconductor switching elements SW3 and SW4 are connected between power supply line PL1 and power supply line NL1 via node N1b, forming a second arm 112. Node N1b is connected to AC terminal 123b.

[0028] Similarly, the secondary-side bridge circuit 120 forms a single-phase full-bridge. Specifically, the secondary-side bridge circuit 120 includes semiconductor switching elements SW5-SW8 connected between the high-potential power supply line PL2 and the low-potential power supply line NL2. Power supply lines PL2 and NL2 are connected to the secondary-side DC terminals 102c and 102d, respectively. A smoothing capacitor 160 is connected between power supply lines PL2 and NL2 to stabilize the secondary-side DC voltage Vdc2.

[0029] Semiconductor switching elements SW5 and SW6 are connected in series between power supply lines PL2 and NL2 via node N2a connected to AC terminal 124a, forming third arm 121. Similarly, semiconductor switching elements SW7 and SW8 are connected in series between power supply lines PL2 and NL2 via node N2b connected to AC terminal 124b, forming fourth arm 122. In first through fourth arms 111, 112, 121, and 122, semiconductor switching elements SW1, SW3, SW5, and SW7 form the "upper arm," while semiconductor switching elements SW2, SW4, SW6, and SW8 form the "lower arm." Hereinafter, semiconductor switching elements SW1 through SW8 will be collectively referred to as semiconductor switching element SW.

[0030] The semiconductor switching element SW comprises a self-extinguishing switching element and a diode. The switching element can be any self-extinguishing element, such as an IGBT (Insulated Gate Bipolar Transistor), a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), or a GCT (Gate Commutated Turn-off) thyristor. The diode is connected in antiparallel with the switching element to form a freewheeling diode (FWD).

[0031] The inductor element 130 has primary-side AC terminals 130a and 130b connected to the AC terminals 123a and 123b of the primary-side bridge circuit 110, respectively, and secondary-side AC terminals 130c and 130d connected to the AC terminals 124a and 124b of the secondary-side bridge circuit 120, respectively. Figure 1 In the example of FIG, the inductor element 130 is formed by a transformer 11 having a primary winding 11 a connected between primary-side AC terminals 130 a and 130 b and a secondary winding 11 b connected between secondary-side AC terminals 130 c and 130 d.

[0032] Figure 2 is a diagram showing an equivalent circuit of the inductor element 130. Figure 2 As shown in FIG. 1 , the inductance element 130L may also be configured to include a reactor 11c connected between the primary side AC terminal 130a and the secondary side AC terminal 130c. Figure 2 The inductor element 130L shown in FIG. 1 can be used as an equivalent circuit of the aforementioned inductor element 130. Figure 2 Although one of the circuits is an unbalanced circuit, it can also be set as a balanced circuit provided in both circuits.

[0033] return Figure 1 Voltage detector 171 detects the voltage between the terminals of smoothing capacitor 150, that is, primary-side DC voltage Vdc1, and outputs a signal indicating the detected value to control device 103. Voltage detector 172 detects the voltage between the terminals of smoothing capacitor 160, that is, secondary-side DC voltage Vdc2, and outputs a signal indicating the detected value to control device 103.

[0034] The current detector 141 detects AC current IL1 (hereinafter also referred to as “primary AC current”) flowing between the AC terminal 123a of the primary-side bridge circuit 110 and the primary-side AC terminal 130a of the inductor element 130 , and outputs a signal indicating the detection value to the control device 103 .

[0035] The current detector 142 detects AC current IL2 (hereinafter also referred to as “secondary AC current”) flowing between the AC terminal 124a of the secondary bridge circuit 120 and the secondary AC terminal 130c of the inductor 130 , and outputs a signal indicating the detection value to the control device 103 .

[0036] In the following description, the direction of primary-side AC current IL1 flowing from primary-side bridge circuit 110 toward inductor 130 is considered the positive direction. Furthermore, the direction of secondary-side AC current IL2 flowing from secondary-side bridge circuit 120 toward inductor 130 is considered the positive direction.

[0037] Furthermore, the above-mentioned current detector may be either the current detector 141 or the current detector 142. For example, the current detector 141 may be provided on the primary side.

[0038] Control device 103 controls power conversion in DC / DC converter 102. Specifically, control device 103 generates control signals (gate signals) GP1 to GP8 for controlling the on and off of semiconductor switching elements SW1 to SW8 based on commands from a higher-level controller (not shown) and output signals from voltage detectors 171 and 172 and current detector 141.

[0039] For example, the control device 103 can be configured as a microprocessor including a CPU (Central Processing Unit) 103a, a memory 103b, and an input / output (I / O) circuit 103c. The I / O circuit 103a receives input from detection values ​​of sensors disposed on the DC / DC converter 102 and outputs control signals for the components of the DC / DC converter 102. These control signals include the gate signals GP1 to GP8 described above.

[0040] The control device 103 can realize the control functions described below by software processing in which the CPU 103a executes arithmetic processing based on a program stored in the memory 103b. Alternatively, the control device 103 can realize part or all of the control functions by hardware processing using a dedicated electronic circuit.

[0041] The DC / DC converter 102 converts the DC power input from the primary-side DC terminal 102a into AC power (at Figure 1 In the example of the secondary side, the AC power is supplied to the secondary side bridge circuit 120 via the inductor element 130. The secondary side bridge circuit 120 converts the AC power back into DC power and supplies it to the secondary side DC terminals 102c and 102d. In this case, power is supplied from the primary side DC terminals 102a and 102b to the secondary side DC terminals 102c and 102d.

[0042] Alternatively, the DC / DC converter 102 can also transmit power from the secondary-side DC terminals 102c and 102d to the primary-side DC terminals 102a and 102b due to the symmetry of the circuit. In this case, the DC power input to the secondary-side DC terminal 102c is converted into AC power by the secondary-side bridge circuit 120 (in Figure 1(In this example, single-phase AC power is used.) This AC power is transmitted to the primary-side bridge circuit 110 via the inductor element 130. The primary-side bridge circuit 110 converts the AC power back into DC power and transmits it to the primary-side DC terminals 102a and 102b. In this way, the DC power converter 100 can perform DC voltage conversion between the primary and secondary sides, and can also control the power transmission direction to either transmit power from the primary side to the secondary side or from the secondary side to the primary side.

[0043] Next, the operation of the DC power conversion device 100 according to the embodiment will be described.

[0044] Figure 3 This is a diagram for explaining the operation of the DC / DC converter 102 . Figure 3 2 shows the operation when the transformer 11 is used as the inductor element 130 . Figure 3 The horizontal axis represents the switching phase when the switching period Tsw of each semiconductor switch element SW is set to 1 period (2π).

[0045] like Figure 3 As shown, in the primary-side bridge circuit 110, the semiconductor switching elements SW1 and SW2 included in the same branch are turned on and off in a complementary manner. Similarly, the semiconductor switching elements SW3 and SW4 are also turned on and off in a complementary manner. Furthermore, the semiconductor switching elements SW1 and SW4 are turned on and off in phase, and the semiconductor switching elements SW2 and SW3 are turned on and off in phase. The semiconductor switching elements SW1 to SW4 are periodically switched on and off according to the state of the drive signal (gate pulse GP). The above description is for the case where the duty factor of the drive signal is (π / 2), but it is not limited to this and a desired duty factor can be used.

[0046] Similarly, in the secondary-side bridge circuit 120, the semiconductor switching elements SW5 and SW6 included in the same branch are turned on and off in a complementary manner. Similarly, the semiconductor switching elements SW7 and SW8 are also turned on and off in a complementary manner. Furthermore, the semiconductor switching elements SW5 and SW8 are turned on and off in phase, and the semiconductor switching elements SW6 and SW7 are turned on and off in phase. The semiconductor switching elements SW5 to SW8 are periodically switched on and off every (π / 2) of the switching period Tsw, depending on the state of the drive signal (gate pulse GP).

[0047] A phase difference δ (0≦δ≦π) is provided between the timing of switching the semiconductor switch elements SW1 to SW4 on and off in the primary-side bridge circuit 110 and the timing of switching the semiconductor switch elements SW5 to SW8 on and off in the secondary-side bridge circuit 120 .

[0048] By controlling the on / off of the semiconductor switching elements SW1 to SW8 in the primary-side bridge circuit 110 and the secondary-side bridge circuit 120, an AC voltage Vtrpri (hereinafter also referred to as "primary-side AC voltage") is generated between the primary-side AC terminals 130a and 130b of the inductor element 130 (at both ends of the primary winding 11a), and an AC voltage Vtrsec (hereinafter also referred to as "secondary-side AC voltage") is generated between the secondary-side AC terminals 130c and 130d of the inductor element 130 (at both ends of the secondary winding 11b).

[0049] The current flowing through secondary winding 11b is referred to as secondary-side AC current IL2, and the current flowing through primary winding 11a is referred to as primary-side AC current IL1. When the transformer's turns ratio is 1, primary-side AC current IL1 and secondary-side AC current IL2 are equal in magnitude but opposite in direction. This relationship is expressed in the following equation.

[0050] IL1=-IL2

[0051] The primary-side AC current IL1 and the secondary-side AC current IL2 are collectively referred to as the reactor current IL.

[0052] The primary-side AC voltage Vtrpri and the secondary-side AC voltage Vtrsec each become a square wave voltage having a voltage pulse width θ corresponding to the on-period length of the semiconductor switching elements SW1 to SW8 (0≦θ≦π). In this specification, the ratio of the on-period length of the semiconductor switching element SW to the switching period Tsw is defined as the duty cycle.

[0053] Next, the power conversion control by the control device 103 will be described.

[0054] Figure 4A This is a block diagram of the control device 103 of the DC power conversion device 100 according to the embodiment. Figure 4B This is a diagram for explaining a calculation formula used by the control device 103 according to the embodiment. Figure 5 This is a diagram for explaining a current waveform generated by control according to the embodiment.

[0055] The following description Figure 4A The functions of the modules in the block diagrams are represented by at least one of software processing and hardware processing of the control device 103 .

[0056] The control device 103 includes, for example, a voltage detection unit 301 , a phase difference generation unit 302 , a limit value adjustment unit 303 , a limiter 304 , a phase difference command generation unit 305 , a current control unit 306 , and a current detection unit 307 .

[0057] The voltage detection unit 301 receives the voltage from the voltage detectors 171 and 172 ( Figure 1 ). Voltage detection unit 301 samples the detection value of primary-side DC voltage Vdc1 by voltage detector 171 at a predetermined sampling period Tsa and outputs a primary-side DC voltage detection value Vdc1_det based on the sampled value. Voltage detection unit 301 samples the detection value of secondary-side DC voltage Vdc2 by voltage detector 172 at a sampling period Tsa and outputs a secondary-side DC voltage detection value Vdc2_det based on the sampled value.

[0058] The phase difference generating unit 302 includes, for example, a voltage reference generating unit 3021 , a subtractor 3022 , a voltage control unit 3023 , a phase difference conversion gain calculating unit 3024 , a gain adjusting unit 3025 , and a phase calculating unit 3026 .

[0059] The voltage reference generator 3021 receives the primary-side DC voltage detection value Vdc1_det from the voltage detector 301 and generates a voltage reference based on the primary-side DC voltage detection value Vdc1_det. For example, the voltage reference generator 3021 performs a smoothing process on the primary-side DC voltage detection value Vdc1_det and outputs the resulting primary-side DC voltage reference Vdc1_ref.

[0060] The subtractor 3022 calculates the difference between the primary-side DC voltage reference Vdc1_ref supplied from the voltage reference generator 3021 and the secondary-side DC voltage detection value Vdc2_det supplied from the voltage detector 301 as a voltage command.

[0061] Voltage control unit 3023 performs a PI operation on the output of subtractor 3022 (voltage command) to generate a power command Pref. For example, voltage control unit 3023 generates a power command Pref such that the difference between the primary-side DC voltage reference Vdc1_ref provided by voltage reference generator 3021 and the secondary-side DC voltage detection value Vdc2_det provided by voltage detector 301 is zero. This power command Pref corresponds to the power transferred between the primary and secondary sides.

[0062] The phase difference conversion gain calculation unit 3024 calculates a phase difference conversion gain based on the primary-side DC voltage reference Vdc1_ref and the secondary-side DC voltage detection value Vdc2_det.

[0063] Gain adjustment unit 3025 uses the phase difference conversion gain to normalize the power command generated by voltage control unit 3023. More specifically, gain adjustment unit 3025 divides the power command by the phase difference conversion gain (quotient) as the phase adjustment amount.

[0064] Phase calculation unit 3026 uses the phase adjustment amount generated by gain adjustment unit 3025 to adjust the reference phase. For example, phase calculation unit 3026 subtracts the phase adjustment amount from a reference value (e.g., "1") and calculates the square root of the result as a first reference phase. Furthermore, phase calculation unit 3026 subtracts the first reference phase from the reference value (e.g., "1") to calculate a second reference phase.

[0065] As a result, the phase difference generating unit 302 outputs the above-mentioned second reference phase as a calculation result.

[0066] Furthermore, the aforementioned phase difference generating unit 302 generates a command value that creates a phase difference between the primary-side AC voltage Vtrpri and the secondary-side AC voltage Vtrsec. Since AC currents IL1 and IL2 vary according to the phase difference δ, the power transferred between the primary and secondary sides also varies. Therefore, by setting the phase difference δ based on the power command value, the power transferred between the primary and secondary sides can be controlled based on the power command value.

[0067] The transmission power P converted by the DC / DC converter 102 is expressed by the following equation (A) using the switching frequency fsw of the semiconductor switching element SW, the inductance component L of the transformer 11 , and the phase difference δ.

[0068] P=Vdc1·Vdc2 / (2π×fsw×L)·δ·(π-δ)…(A)

[0069] When the above equation (1) is solved for the phase difference δ, it is transformed into the following equation (B).

[0070] δ=

[0071] (π / 2)±(π / 2)·√(1-(8L·fsw·P) / (Vdc1·Vdc2))…(B)

[0072] For example, if the phase difference δ is equal to or smaller than (π / 2), the phase difference command value δref, which is a command value of the phase difference δ, can be calculated from the power command value Pref according to the following formula (C).

[0073] δref=(π / 2)-(π / 2)·√(1-(8L·fsw·Pref) / (Vdc1·Vdc2))…(C)

[0074] Therefore, the limit value adjustment unit 303 , the limiter 304 , the phase difference command generation unit 305 , the current control unit 306 , and the current detection unit 307 can be configured as follows.

[0075] The current detection unit 307 receives, for example, the current detector 141 ( Figure 1The current detection unit 307 samples the output signal of the current detector 141 at a sampling period Tsa and outputs a current detection value IL1_det based on the sampled value.

[0076] The limit value adjustment unit 303 receives the primary-side DC voltage reference Vdc1_ref, the secondary-side DC voltage detection value Vdc2_det, and the current detection value IL1_det, and generates a limit value φ_LMT.

[0077] The limit value adjustment unit 303 includes, for example, limit value calculation units 3031 and 3032 and a limit value determination unit 3033 .

[0078] The limit value calculation unit 3031 is based on Figure 4B The first limit value φ(t2) is calculated using the calculation formula (1) shown.

[0079] The limit value calculation unit 3032 is based on Figure 4B The second limit value φ(t3) is calculated using the calculation formula (2) shown.

[0080] The details of equations (1) and (2) will be described later.

[0081] The limit value determination unit 3033 determines the limit value φ_LMT based on the first limit value φ(t2) and the second limit value φ(t3). For example, the limit value determination unit 3033 selects the smaller of the first limit value φ(t2) and the second limit value φ(t3).

[0082] When the second reference phase generated by the phase difference generating unit 302 is excessively larger than the limit value φ_LMT, the limiter 304 limits the magnitude of the second reference phase so as to be equal to or smaller than the limit value φ_LMT.

[0083] The phase difference command generating unit 305 divides the output value from the limiter 304 by 2 to calculate a phase difference command value δref (phase shift command δref).

[0084] The current control unit 306 uses the phase difference command value δref to implement phase shift control based on the DAB method, sets the phase difference according to the phase shift command δref, generates gate pulses GP1-GP8 for driving the DC / DC converter 102, and supplies them to the primary-side bridge circuit 110 and the secondary-side bridge circuit 120.

[0085] Thus, the DC / DC converter 102 operates the primary-side bridge circuit 110 and the secondary-side bridge circuit 120 using the gate pulses GP1 - GP8 .

[0086] If the control in the DC / DC converter 102 is in a stable state, then as described above Figure 3As shown, the waveform of the reactor current is a repetition of waveforms of the same shape. Figure 5 Indicates the situation of one cycle.

[0087] Determine the following Figure 5 The waveform of the reactor current shown is characterized by various parameters.

[0088] The primary-side DC voltage detection value Vdc1_det and the secondary-side DC voltage detection value Vdc2_det are treated as voltages applied to the primary-side winding and the secondary-side winding of the transformer, and are abbreviated as V1 and V2.

[0089] The voltage V2 on the secondary side of the transformer is converted to the voltage V1 on the primary side using a coefficient kn based on the turns ratio, which is recorded as V2'.

[0090] V2'=knV2 (where kn=n1 / n2, n1 and n2 are the number of turns on the primary side and the number of turns on the secondary side)

[0091] Figure 5 t0, t1, t2, and t3 on the horizontal axis represent the timings at which the control modes are started. Each control mode is started at these timings. The order of the control modes is Mode 1-1, Mode 1-2, Mode 2, and Mode 3.

[0092] t0: Mode 1-1 start time

[0093] t1: Mode 1-2 start time

[0094] t2: Mode 2 start time

[0095] t3: Mode 3 start time

[0096] In addition, when the above-mentioned control mode is switched, there is actually a time (control mode) for charging and discharging a capacitor (not shown), but the description thereof is omitted for simplicity of explanation.

[0097] The magnitudes of the reactor currents at times t0, t1, t2, and t3 are denoted as i(t0), i(t1), i(t2), and i(t3), respectively.

[0098] i(t0): Reactor current at time t0

[0099] i(t1): Reactor current at time t1

[0100] i(t2): Reactor current at time t2

[0101] i(t3): Reactor current at time t3

[0102] T represents the period, and T1 and T2 represent the duration of each control mode.

[0103] T: period

[0104] T1: Duration of Mode 1 (combination range of Mode 1-1 and Mode 1-2)

[0105] T2: Duration of Mode 2

[0106] The angle corresponding to the duration T1 of Mode 1 is represented by δ. The angle corresponding to the duration T2 of Mode 2 is (2Dπ - δ). Furthermore, (2Dπ) is the angle corresponding to the pulse width of gate pulses GP1-GP8 with a duty factor of D.

[0107] δ: Angle [rad] corresponding to the duration T1 of Mode 1 when the angle of one cycle is set to 2π [rad] (equivalent to the phase difference)

[0108] (2Dπ-δ): Angle corresponding to the duration T2 of Mode 2 [rad]

[0109] D:Duty Factor

[0110] ΔIL1: Reactor current change during Mode 1

[0111] ΔIL2: Reactor current change during Mode 2

[0112] i(t0)=-i(t3)

[0113] i(t1)=0

[0114] i(t2)=i(t3)-ΔIL2

[0115] i(t3)=(ΔIL1+ΔIL2) / 2

[0116] During Mode 1, (V1 + V2') is applied to the equivalent reactor. This relationship is expressed as follows.

[0117] ΔIL1=(V1+V2')T1 / L

[0118] During Mode 2, (V1-V2') is applied to the equivalent reactor. This relationship is expressed as follows.

[0119] ΔIL2=(V1-V2')T2 / L

[0120] ΔIL2 can take positive or negative values ​​depending on the size of V1 and V2'. For example, if V2' is greater than V1, the value of ΔIL2 is negative, and power is transferred from the secondary side to the primary side. The current waveform in this state becomes Figure 5 In contrast, if V2' is less than V1, the value of ΔIL2 is positive, and power is transferred from the primary side to the secondary side. The current waveform in this state is similar to Figure 5 The waveform shown is different in that the current increases during the Mode 2 period from time t2 to t3.

[0121] When the left sides and right sides of the two equations related to ΔIL1 and ΔIL2 are added together, the following equations are obtained.

[0122] ΔIL1+ΔIL2=(V1+V2')T1 / L+(V1-V2')T2 / L=((T1+T2)V1+(T1-T2)V2') / L

[0123] With respect to T1 and T2, the following equation holds.

[0124] T1=(δ / 2π)T=δ / ω

[0125] T2=((2Dπ-δ) / 2π)T=(2Dπ-δ) / ω

[0126] Substituting T1 and T2 into the above equation, we get the following equation.

[0127] ΔIL1+ΔIL2=(2DπV1+(2δ-2Dπ)V2') / (ωL)=2(DπV1+(δ-Dπ)V2') / (ωL)

[0128] Therefore, i(t2) and i(t3) can be respectively arranged as follows.

[0129] i(t2)=i(t3)-ΔIL2=((2δ-π)V1+πV2') / (2ωL)

[0130] i(t3)=(ΔIL1+ΔIL2) / 2=(DπV1+(2δ-Dπ)V2') / (2ωL)

[0131] exist Figure 5 During Mode 1, the following relationship exists. This is obtained through triangle similarity.

[0132] (t1-t0): (t2-t1)=-i(t0):i(t2)=i(t3):i(t2)

[0133] t1-t0=T1×i(t3) / (i(t2)+i(t3))

[0134] t2-t1=T1×i(t2) / (i(t2)+i(t3))

[0135] Taking t0 as the starting point of time and phase, the above equations are simplified and the main equations are listed below.

[0136] t1=T1×i(t3) / (i(t2)+i(t3))

[0137] t2=T1

[0138] t3=T1+T2

[0139] T1=δ / ω

[0140] T2=(2Dπ-δ) / ω

[0141] i(t0)=-i(t3)

[0142] i(t1)=0

[0143] i(t2)=((2δ-π)V1+πV2') / (2ωL)

[0144] i(t3)=(DπV1+(2δ-Dπ)V2') / (2ωL)=(DπV1+(2δ-Dπ)(kn)V2) / (2ωL)

[0145] V2' = (kn) V2 (where kn = n1 / n2)

[0146] ω=2πf

[0147] If the value of D, i.e. the duty cycle, is set to 0.5, we can get Figure 4B The formula shown.

[0148] In this manner, in DAB control, the peak value of the current flowing through the transformer winding can be determined based on the primary-side DC voltage Vdc1 and the secondary-side DC voltage Vdc2 , the transformer inductance, the transformer turns ratio, and the phase difference δ.

[0149] As described above, the peak value of the current flowing through the winding of the transformer changes according to the primary-side DC voltage Vdc1 , the secondary-side DC voltage Vdc2 , and the phase difference δ.

[0150] Figure 6 This is a diagram for explaining an example of a current waveform.

[0151] For example, when the current flowing in the transformer winding is set to Figure 6 When the amplitude of the waveform shown by the dotted line flows by a phase difference δ, a state occurs in which Mode 2 continues until time t4 corresponding to the phase difference δ.

[0152] In the case of the comparative example, if the flow Figure 6 In the case of the current indicated by the dotted line, current flows through the winding of the transformer and each semiconductor switching element.

[0153] In the case of this embodiment, when the flow Figure 6 Before the current of the dotted line is shown, the phase difference δ is limited at the time point of time t2, so the control of Mode 1 does not continue to exceed the phase difference δ at the time point of time t2, and at the time point of time t2, it switches from Mode 1 to Mode 2. As a result, the peak value of the current flowing in the transformer winding is limited to the same as Figure 5 The same current value as i(t2) is shown.

[0154] Based on the above relationship, limiting the phase difference δ indirectly sets an upper limit on the current value. The upper limit of the phase difference command value δref used in this control is calculated using information about the current primary-side DC voltage Vdc1 and secondary-side DC voltage Vdc2. This allows a limit value based on the upper limit of the current flowing through the transformer winding to be set for the phase difference command value δref in the phase shift control method.

[0155] By implementing this control, the current flowing through the transformer windings can be limited to a value that does not damage the device. This design can suppress device damage caused by overcurrent. Furthermore, the accuracy of estimating the actual maximum current flowing is improved, allowing for further optimization of overcurrent derating. Based on these research results, by selecting a design strategy that suppresses maximum current, the range of semiconductor switching elements available can be expanded, further enabling the miniaturization of DC power conversion devices.

[0156] According to the above-described embodiment, the DC power conversion device 100 performs DAB-based power conversion control for transmitting power between the first DC power and the second DC power.

[0157] The first bridge circuit 110 of the DC power converter 100 is driven by gate pulses GP1-4 (first drive signal) to convert first DC power at a first DC voltage into first AC power and output it to a first AC terminal. The second bridge circuit 120 is driven by gate pulses GP5-8 (second drive signal) to convert second DC power at a second DC voltage into second AC power and output it to a second AC terminal.

[0158] The inductor element 130 is disposed between the first bridge circuit 110 and the second bridge circuit 120 and is connected to the first AC terminal and the second AC terminal respectively.

[0159] The control device 103 determines a phase difference between the first drive signal and the second drive signal used in phase shift control of the DAB method, generates the first drive signal and the second drive signal for driving the first bridge circuit 110 and the second bridge circuit 120 based on the phase difference, and drives the first bridge circuit 110 and the second bridge circuit 120 using the first drive signal and the second drive signal.

[0160] The control device 103 generates the first drive signal and the second drive signal that limit the phase difference to the allowable range by using the first DC voltage and the second DC voltage to determine the allowable range of the phase difference and limit the magnitude of the current flowing in the inductor element 130.

[0161] Thus, the DC power conversion device 100 can reduce the influence of voltage fluctuations occurring between the input voltage and the output voltage of the DAB DC power conversion device.

[0162] In addition, the control device 103 may determine the allowable range based on the first DC voltage, the second DC voltage, and the magnitude of the current flowing in the inductor 130 .

[0163] The inductor element 130 may be configured to include a transformer.

[0164] For example, the control device 103 may determine a limit value for limiting the magnitude of the phase difference using the first DC voltage, the second DC voltage, the inductance of the inductor element 130 (transformer), and the turns ratio of the transformer.

[0165] Alternatively, the control device 103 may estimate the magnitude of the current flowing in the inductor 130 using the first DC voltage, the second DC voltage, the inductance of the inductor (transformer), the turns ratio of the transformer, and the magnitude of the phase difference.

[0166] Furthermore, for example, in the control device 103, the phase difference generator 302 outputs the aforementioned second reference phase as a calculation result. The limit value adjuster 303 calculates a first limit value φ(t2) and a second limit value φ(t3), and determines a limit value φ_LMT based on the magnitude of the first limit value φ(t2) and the second limit value φ(t3). The limiter 304 increases the generated second reference phase if it is not larger than the limit value φ_LMT. If it is larger than the limit value φ_LMT, the limiter 304 limits the magnitude of the second reference phase to be equal to or smaller than the limit value φ_LMT. For example, after the phase difference command generator generates the phase difference command value δref based on the output of the limiter 304, the current controller 306 can use the phase difference command value δref to implement DAB phase shift control.

[0167] More specifically, the first limit value calculation unit 3031 of the limit value adjustment unit 303 calculates a first limit value φ(t2) for phase shift control. The first limit value calculation unit 3032 calculates a second limit value φ(t3) for phase shift control. The limit value determination unit 3033 can determine the limit value φ_LMT based on the magnitude of the first limit value φ(t2) and the second limit value φ(t3).

[0168] (Variation 1)

[0169] Modification 1 of the embodiment will be described.

[0170] In the above embodiment, as Figure 3 The duty ratio of the drive signal (gate pulse) shown in FIG. 1 is 0.5. Alternatively, the duty ratio may be set to a value other than 0.5. In this case, an equation including the duty ratio value (D) may be used as the calculation formula for determining the limit value of the phase difference command value δref.

[0171] The duty ratio value (D) may be a predetermined value (constant) or a variable whose value is set according to the control state. The most recent duty ratio value (D) when determining the limit value of the phase difference command value δref described above may be used.

[0172] (Variation 2)

[0173] Modification 2 of the embodiment will be described.

[0174] In the above embodiment, the description of the transformer excitation current is omitted, and the influence of the load current is discussed as the center. In addition, by considering the influence of the transformer excitation current, the accuracy can be further improved.

[0175] For example, if a current with a DC component superimposed on it flows through a transformer, causing bias magnetization, a current exceeding normal current may flow through the transformer windings. If this occurs, even for a transformer with a turns ratio of 1, a difference may occur between the AC currents IL1 and IL2.

[0176] Therefore, the AC current IL1 and the AC current IL2 are detected separately, and the limit value of the phase difference command value δref can be determined based on the AC current IL1 and the AC current IL2.

[0177] For example, a representative value of either the detected value of AC current IL1 or the detected value of AC current IL2 can be used to calculate the limit value of phase difference command value δref. As the representative value, the larger of the detected value of AC current IL1 or the detected value of AC current IL2, or the average of these two values ​​can be used.

[0178] According to at least one embodiment described above, a DC power converter performs power conversion between first and second DC powers using a DAB method for transferring power between the first and second DC powers. The DC power converter includes a first bridge circuit, a second bridge circuit, an inductor element, and a control device. The first bridge circuit is driven by a first drive signal to convert the first DC power into first AC power and output it to a first AC terminal. The second bridge circuit is driven by a second drive signal to convert the second DC power having a second DC voltage into second AC power and output it to a second AC terminal. The inductor element is disposed between the first and second bridge circuits and is connected to the first and second AC terminals, respectively. The control device determines a phase difference between the first and second drive signals used in phase shift control using the DAB method, generates the first and second drive signals for driving the first and second bridge circuits based on the phase difference, and drives the first and second bridge circuits using the first and second drive signals. The control device can reduce the influence of voltage fluctuations generated between the input voltage and the output voltage of the DAB type DC power conversion device by generating the first drive signal and the second drive signal that limit the phase difference within the allowable range while using the first DC voltage and the second DC voltage to determine the allowable range of the phase difference and limit the magnitude of the current flowing in the inductor element.

[0179] In the DC power conversion device 100 of the embodiment described above, some or all of the functional units of the control device 103 may be implemented as software functional units, for example, by executing a program (computer program, software component) stored in a storage unit (memory, etc.) of the computer by a computer processor (hardware processor). In addition, some or all of the functional units of the control device 103 may be implemented as hardware such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), or an FPGA (Field-Programmable Gate Array), or may be implemented as a combination of software functional units and hardware.

[0180] Several embodiments of the present invention have been described, but these embodiments are provided as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the main purpose of the invention. For example, the structures of the various embodiments can also be combined with each other to implement and can be applied to components that have been omitted from the description. These embodiments and their variations are included in the scope and main purpose of the invention, and are included in the invention described in the claims and their equivalents.

[0181] Description of Reference Numerals

[0182] 100…DC power conversion device;

[0183] 102…DC / DC converter;

[0184] 103…control device;

[0185] 110…primary side bridge circuit;

[0186] 120…Secondary side bridge circuit;

[0187] 130…Inductor components;

[0188] 150, 160... smoothing capacitors;

[0189] 301 ... voltage detection unit;

[0190] 302 ...phase difference generating unit;

[0191] 303 ...limit value adjustment unit;

[0192] 304…Limiter;

[0193] 305 ...phase difference instruction generating unit;

[0194] 306 ...current control unit;

[0195] 307 ...current detection unit;

[0196] 3031, 3032: limit value calculation unit (first limit value calculation unit, second limit value calculation unit);

[0197] 3033…Limit value determination unit.

Claims

1. A DC power converter that performs DAB-based power conversion control for transmitting power between a first DC power and a second DC power, comprising: a first bridge circuit, driven by a first drive signal, converting first DC power of a first DC voltage into first AC power and outputting the power to a first AC terminal; a second bridge circuit, driven by a second drive signal, converting a second DC power of a second DC voltage into a second AC power and outputting the power to a second AC terminal; an inductor element, disposed between the first bridge circuit and the second bridge circuit, and connected to the first AC terminal and the second AC terminal respectively; as well as a control device that determines a phase difference between the first drive signal and the second drive signal used in phase shift control in a DAB system, generates the first drive signal and the second drive signal for driving the first bridge circuit and the second bridge circuit respectively based on the phase difference, and drives the first bridge circuit and the second bridge circuit using the first drive signal and the second drive signal. The control device is: When the first DC voltage and the second DC voltage are used to determine an allowable range of the phase difference and to limit the magnitude of the current flowing in the inductor element, the first drive signal and the second drive signal are generated so as to limit the phase difference to the allowable range.

2. The DC power conversion device according to claim 1, wherein: The control device determines the allowable range based on the first DC voltage, the second DC voltage, and the magnitude of the current flowing through the inductor element.

3. The DC power conversion device according to claim 1, wherein: The inductor element is configured to include a transformer, The control device determines a limit value for limiting the magnitude of the phase difference using the first DC voltage, the second DC voltage, the inductance of the inductor element, and the turns ratio of the transformer.

4. The DC power conversion device according to claim 1, wherein: The inductor element is configured to include a transformer, The control device estimates the magnitude of the current flowing in the inductance element using the first DC voltage, the second DC voltage, the inductance of the inductance element, the turns ratio of the transformer, and the magnitude of the phase difference.

5. The DC power conversion device according to claim 1, wherein: The control device includes a phase difference generating unit, a limit value adjusting unit, a limiter, a phase difference command generating unit, and a current control unit. The phase difference generating unit outputs the second reference phase as a calculation result. The limit value adjustment unit calculates a first limit value and a second limit value, and determines the limit value based on the magnitude of the first limit value and the second limit value. The limiter (304) increases the generated second reference phase when the generated second reference phase is not larger than the limit value, and limits the magnitude of the second reference phase to be smaller than the limit value when the generated second reference phase is larger than the limit value. The phase difference command generating unit generates a phase difference command value according to the output of the limiter. The current control unit performs DAB phase shift control using a phase difference command value.

6. The DC power conversion device according to claim 5, wherein: The limit value adjustment unit includes a first limit value calculation unit, a second limit value calculation unit, and a limit value determination unit. The first limit value calculation unit calculates a first limit value for the phase shift control. The first limit value calculation unit calculates the second limit value of the phase shift control, The limit value determination unit (3033) determines the limit value based on the magnitude of the first limit value and the second limit value.

7. A control method for a DC power converter, comprising performing DAB power conversion control for transmitting power between a first DC power and a second DC power. The DC power conversion device has: a first bridge circuit, driven by a first drive signal, converting first DC power of a first DC voltage into first AC power and outputting the power to a first AC terminal; a second bridge circuit, driven by a second drive signal, converting a second DC power of a second DC voltage into a second AC power and outputting the power to a second AC terminal; as well as an inductor element, disposed between the first bridge circuit and the second bridge circuit, and connected to the first AC terminal and the second AC terminal respectively; In the control method, determining a phase difference between the first drive signal and the second drive signal used in phase shift control in a DAB system, generating the first drive signal and the second drive signal for driving the first bridge circuit and the second bridge circuit, respectively, based on the phase difference, and driving the first bridge circuit and the second bridge circuit using the first drive signal and the second drive signal; When the first DC voltage and the second DC voltage are used to determine an allowable range of the phase difference and to limit the magnitude of the current flowing in the inductor element, the first drive signal and the second drive signal are generated so as to limit the phase difference to the allowable range.

8. The control method according to claim 7, wherein: The allowable range is determined based on the first DC voltage, the second DC voltage, and the magnitude of the current flowing in the inductor element.

9. The control method according to claim 7, wherein: The inductor element is configured to include a transformer, A limit value for limiting the magnitude of the phase difference is determined using the first DC voltage, the second DC voltage, the inductance of the inductor element, and the turns ratio of the transformer. The first drive signal and the second drive signal are generated.

10. The control method according to claim 7, wherein: The inductor element is configured to include a transformer, The magnitude of the current flowing in the inductor element is estimated using the first DC voltage, the second DC voltage, the inductance of the inductor element, the turns ratio of the transformer, and the magnitude of the phase difference.

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