Four-phase floating interleaved bidirectional dc-dc converter

Abstract

The application provides a bidirectional DC-DC converter, which can realize DC bus voltage operation in a wide range of boost / buck voltage ratio and inductance current balance, and further improve the voltage ratio and output power. The bidirectional DC-DC converter is composed of a pair of two-phase interleaved charge pump. The positive and negative poles of the low-voltage side of each DC-DC converter are connected in parallel with the low-voltage side DC bus, and one end of the high-voltage side is connected with the positive and negative poles of the high-voltage side DC bus, respectively, and the other end is in a floating state. The high-voltage side voltage is the voltage formed by the superposition of the charge pump capacitor voltage of each DC-DC converter and the low-voltage side voltage. In the driving circuit (2), the error amplification value of the synthesized value of the four-phase inductance current and the reference value is asymmetrically set to the upper limit or lower limit limit value of the duty cycle of the driving pulse of the part switch as the control object in the buck mode / boost mode, respectively.

Description

Technical Field

[0001] This invention relates to an interleaved charge pump bidirectional DC-DC converter with a wide range of buck / boost voltage ratios. Background Technology

[0002] In recent years, bidirectional converters have played a crucial role in DC microgrid systems that connect DC energy sources such as electric vehicles (EVs) and energy storage units to DC buses. For example... Figure 14 As shown, in power conditioning devices for photovoltaic (PV) power generation or V2G systems that connect electric vehicles (EVs) to the power system, a bidirectional DC-DC converter capable of bidirectional power transfer between two DC voltage sources with a large potential difference is required.

[0003] In DC microgrid systems connected to electric vehicles (EVs), the DC bus voltage is typically between 200V and 380V, while the EV battery voltage is generally between 400V and 800V. On the other hand, the voltage range of energy storage systems is typically from tens of volts to thousands of volts. Therefore, as the energy interface between the energy storage system and the EV battery, a bidirectional DC-DC converter with a wide voltage conversion ratio is required to meet the needs of DC microgrid systems connected to EVs.

[0004] To improve the power capacity (operating current) and reduce the current ripple of the low-voltage side inductor in bidirectional DC-DC converters, an intermittently driven (alternated) two-phase converter circuit is typically employed. Alternated bidirectional DC-DC converters effectively reduce inductor current ripple and optimize overall efficiency while increasing power ratings, thus they are widely used in bidirectional DC-DC converter applications. However, due to differences in power device characteristics and circuit parameter deviations, current imbalance problems can easily arise, necessitating the introduction of current balancing control. Furthermore, in traditional technologies, the duty cycle of power devices is typically limited to no more than 50%, which not only makes current balancing difficult to achieve but also restricts the voltage conversion range of the converter, thus limiting its application scenarios.

[0005] To achieve bidirectional power conversion, the interleaved bidirectional DC-DC converter (IBDC) has been extensively studied. However, the voltage ratio range of IBDC is limited, making it only suitable for applications where the input and output voltage variations are small. To overcome the shortcomings of IBDC, the interleaved charge-pump bidirectional DC-DC converter (ICPBDC) (Non-Patent Literature 1) has been proposed.

[0006] ICPBDC has a better voltage conversion ratio than IBDC, theoretically twice that of IBDC. Specifically, since the boost-to-buck ratio is limited by the duty cycle of the switch, the upper limit of the boost ratio is approximately 20 times (when the duty cycle is 0.9), and the lower limit of the buck ratio is 0.05 times (when the duty cycle is 0.1).

[0007] While ICPBDC offers advantages in reducing input current ripple and increasing system power capacity, it still has limitations. Specifically, it relies on the duty cycle of both phase switches being limited to 0.5 (less than 0.5 for buck operation and greater than 0.5 for boost operation). Because it needs to maintain inductor current balance, it can only operate within half of the duty cycle range, thus limiting the converter's wide voltage ratio capability. In other words, in buck operation, the main switch's duty cycle is above 0.5, while in boost operation, it's below 0.5, making it difficult to maintain current balance between the two phases, hindering the achievement of high conversion ratio characteristics. Therefore, the applicable power systems are limited, making it imperative to expand the functionality of the two-phase power converter.

[0008] To address the aforementioned issues, a novel ICPBDC scheme is needed. This scheme should be able to achieve DC bus voltage operation and inductor current equalization across a wide range of boost / buck voltage ratios, while further improving the voltage ratio and output power.

[0009] [Patent Documents]

[0010] [Patent Document 1] Japanese Re-appearance No. 2018 / 066444

[0011] [Non-patent literature]

[0012] [Non-patent document 1] CM Lai, “Development of a Novel Bidirectional DC / DCConverter Topology with High Voltage Conversion Ratio for Electric Vehicles and DC-Microgrids”, Energies, Vol. 9, No. 6, pp.410:1-25, June 2016. Summary of the Invention

[0013] The technical problem that the invention aims to solve

[0014] In view of the above, the present invention aims to provide a bidirectional DC-DC converter that can achieve DC bus voltage operation under a wide range of boost / buck voltage ratios, balance inductor current, and further improve voltage ratio and output power.

[0015] Methods used to solve problems

[0016] To address the aforementioned issues, the bidirectional DC-DC converter of the present invention comprises a pair of two-phase interleaved charge pump bidirectional DC-DC converters. The converter is characterized in that the positive and negative terminals of the low-voltage side of each DC-DC converter are connected in parallel to the low-voltage side DC bus, and one end of the high-voltage side of each DC-DC converter is connected to the positive and negative terminals of the high-voltage side DC bus, while the other end is in a floating state.

[0017] By employing two two-phase interleaved charge pump bidirectional DC-DC converters, with one end of each high-voltage side converter set to a floating state and the other end connected to the high and low sides of the high-voltage side respectively, the low-voltage side voltage can be superimposed on the high-voltage side voltage, which includes the voltages of the two charge pump capacitors, achieving an extremely high voltage ratio. Therefore, the high-voltage side voltage of the DC-DC converter is the voltage obtained by superimposing the voltage of the high-voltage side filter capacitor of each DC-DC converter with the low-voltage side voltage of the DC-DC converter. Furthermore, the high-voltage side voltage V... H With low-voltage side voltage V L The voltage ratio, when the duty cycle of the DC-DC converter switch is D, satisfies V in buck mode. L / V H = D / (4-D), which satisfies V in boost mode. H / V L = (3+D) / (1-D). Moreover, higher output power capacity can be easily achieved through interleaved drive.

[0018] Here, a two-phase interleaved charge pump bidirectional DC-DC converter is described. Two-phase interleaved refers to the two inductors within the converter operating alternately with a 180° phase difference to cancel the ripple current of the input-side capacitor. Furthermore, the charge pump refers to the charge pump capacitor in the converter, used to achieve a higher boost ratio and buck ratio. A bidirectional DC-DC converter employing a two-phase interleaved configuration and incorporating a charge pump as a component is defined in this specification as a two-phase interleaved charge pump bidirectional DC-DC converter.

[0019] Furthermore, the floating state refers to the state where the potential is separated from the ground potential. Floating is achieved by the capacitor in the intermediate stage and is considered to have no particular impact on the input-output characteristics of the bidirectional DC-DC converter of this invention. That is, one end of each bidirectional DC-DC converter is connected to one end of the input / output port, and additionally, through the low-voltage side filter capacitor (C... L The connection is considered to have no effect because the low-voltage connection is on the low side.

[0020] In the bidirectional DC-DC converter of the present invention, in a pair of DC-DC converters, the upper or lower limit of the duty cycle of the drive pulse of the part of the switch that is the control object is set to limit the amplified value of the error between the synthesized value of the four-phase inductor current and its reference value, respectively in boost mode and buck mode, and the switching operation is performed.

[0021] This improves the voltage conversion ratio applicable to a wide input / output range. Specifically, in a pair of DC-DC converters, simple duty cycle limiting control is achieved by setting upper or lower limits on the duty cycle of the drive pulses for some switches of the controlled object in boost and buck modes, respectively. This control method enables uncontrolled inductor current balance, low conduction losses, low switching stress, high-speed transient response, and high power density. This duty cycle limiting control can be implemented with simple control logic using low-cost analog control circuits or digital control processors.

[0022] The bidirectional DC-DC converter of this invention is positioned between the low-voltage side DC bus and the high-voltage side DC bus. A pair (two sets) of bidirectional DC-DC converters employing a two-phase interleaved charge pump structure are connected in parallel on their low-voltage sides. With one pole floating, the other end of each high-voltage side is connected to the positive and negative poles of the high-voltage DC bus, respectively. The bidirectional DC-DC converter of this invention consists of a pair of power semiconductor switches (Q1-Q4 and Q5-Q8) and a charge pump capacitor (C...). 1B and C 2B Inductors (L1, L2 and L3, L4), low-voltage side filter capacitors (C) L ) and high-voltage side filter capacitor (C H1 and C H2 )constitute.

[0023] Furthermore, the switching drive circuit of the DC-DC converter sets an upper limit on the duty cycle of the switching drive pulses of the first switch (Q1) and the fifth switch (Q5) to set a lower limit on the duty cycle of the switching drive pulses of the fourth switch (Q4) and the eighth switch (Q8) to amplify the error between the combined value of the four-phase currents of the first inductor (L1) to the fourth inductor (L4) and the reference value. In addition, the first switch (Q1) and the fifth switch (Q5), the second switch (Q2) and the sixth switch (Q6), the third switch (Q3) and the seventh switch (Q7), and the fourth switch (Q4) and the eighth switch (Q8) are driven with a 90° phase difference between each other.

[0024] First, the DC-DC converter circuit connected to the high side includes the following components 1a) to 1h).

[0025] 1a) The first and second inductors (L1, L2) are connected in parallel to the positive side of the low-voltage DC bus.

[0026] 1b) The second switch (Q2) is connected in series with the first inductor (L1).

[0027] 1c) The first switch (Q1) is connected between the second switch (Q2) and the positive side of the high-voltage DC bus.

[0028] 1d) The third switch (Q3) is connected between the first inductor (L1) and the negative side of the low-voltage DC bus.

[0029] 1e) The fourth switch (Q4) is connected between the second inductor (L2) and the negative side of the low-voltage DC bus.

[0030] 1f) The first high-voltage side filter capacitor (C) connected between the positive terminal of the high-voltage side DC bus and the negative terminal of the low-voltage side DC bus. H1 ).

[0031] 1g) is connected between the positive side of the low-voltage DC bus and the negative side of the low-voltage DC bus. The first high-voltage side filter capacitor (C) H1 ) and its low-voltage side filter capacitor (C) directly connected to its low potential L ).

[0032] 1h) The first charge pump capacitor (C) is connected between the connection point of the first and second switches (Q1, Q2) and the connection point of the second inductor (L2) and the fourth switch (Q4). 1B ).

[0033] Next, the DC-DC converter circuit connected to the low side includes the following components (2a to 2g).

[0034] 2a) The third and fourth inductors (L3, L4) are connected in parallel to the negative side of the low-voltage DC bus.

[0035] 2b) The sixth switch (Q6) is connected in series with the third inductor (L3).

[0036] 2c) The fifth switch (Q5) is connected between the sixth switch (Q6) and the negative side of the high-voltage DC bus.

[0037] 2d) The 7th switch (Q7) is connected between the 3rd inductor (L3) and the positive side of the low-voltage DC bus.

[0038] 2e) The 8th switch (Q8) is connected between the 4th inductor (L4) and the positive side of the low-voltage DC bus.

[0039] 2f) The second high-voltage side filter capacitor (C) connected between the negative terminal of the high-voltage side DC bus and the positive terminal of the low-voltage side DC bus. H2 ).

[0040] 2g) The second charge pump capacitor (C) is connected between the connection point of the 5th and 6th switches (Q5, Q6) and the connection point of the 4th inductor (L4) and the 8th switch (Q8). 2B ).

[0041] In addition, the low-voltage side filter capacitor (C) in the above 1g) L It is not only used for DC-DC converter circuits connected to the high side, but is used by both DC-DC converter circuits connected to the high side and DC-DC converter circuits connected to the low side.

[0042] In the bidirectional DC-DC converter of the present invention, the drive circuit enables the first switch (Q1) and the fourth switch (Q4), the second switch (Q2) and the third switch (Q3), the fifth switch (Q5) and the eighth switch (Q8), and the sixth switch (Q6) and the seventh switch (Q7) to conduct complementaryly.

[0043] (1) In buck mode, switches 1 and 2 (Q1, Q2) are the main switches of the DC-DC converter circuit connected to the high side, while switches 5 and 6 (Q5, Q6) are the main switches of the DC-DC converter circuit connected to the low side. There is a 180° phase difference between switches 1 (Q1) and 2 (Q2), a 180° phase difference between switches 5 (Q5) and 6 (Q6), and a 90° phase difference between switches 1 (Q1) and 5 (Q5).

[0044] (2) In boost mode, switches 3 and 4 (Q3, Q4) are the main switches of the DC-DC converter circuit connected to the envelope, while switches 7 and 8 (Q7, Q8) are the main switches of the DC-DC converter circuit connected to the bottom. There is a 180° phase difference between switches 3 (Q3) and 4 (Q4), a 180° phase difference between switches 7 (Q7) and 8 (Q8), and a 90° phase difference between switches 4 (Q4) and 8 (Q8).

[0045] In the bidirectional DC-DC converter of the present invention, the duty cycle (D) of the switching drive pulse of the first switch (Q1) is... Q1 The duty cycle (D) of the switching drive pulse of the fourth switch (Q4) Q4 The duty cycle (D) of the switching drive pulse of the 5th switch (Q5) Q5 ) and the duty cycle (D) of the switching drive pulse of the 8th switch (Q8) Q8 The voltage remains consistent in both boost and buck modes, and each satisfies 0 < D. Q1 ≤ 0.5, 0.5 ≤ D Q4 < 1、0 < D Q5 ≤ 0.5, 0.5 ≤ D Q8 < 1.

[0046] In addition, the duty cycle (D) of the switching drive pulse of the second switch (Q2) Q2 The duty cycle (D) of the switching drive pulse of the third switch (Q3) Q3 The duty cycle (D) of the switching drive pulse of the 6th switch (Q6) Q6 ) and the duty cycle (D) of the switching drive pulse of the 7th switch (Q7) Q7 The voltage remains consistent in both boost and buck modes, and each satisfies 0 < D. Q1 < 1、0 < D Q3 < 1、0 < D Q6 < 1、0 < D Q7 < 1.

[0047] In the bidirectional DC-DC converter of the present invention, the sum of the duty cycles of the first switch (Q1) and the fourth switch (Q4), the sum of the duty cycles of the second switch (Q2) and the third switch (Q3), the sum of the duty cycles of the fifth switch (Q5) and the eighth switch (Q8), and the sum of the duty cycles of the sixth switch (Q6) and the seventh switch (Q7) are all 1.

[0048] Then, in buck mode, the following 1) is used, and in boost mode, the following 2) is used.

[0049] 1) In step-down mode: When the duty cycle of the second switch (Q2) and the sixth switch (Q6) is less than 0.5, the duty cycles of the first switch (Q1), the second switch (Q2), the fifth switch (Q5), and the sixth switch (Q6) are the same; when the duty cycle of the second switch (Q2) and the sixth switch (Q6) is greater than or equal to 0.5, the duty cycle of the first switch (Q1) and the fifth switch (Q5) is fixed at 0.5.

[0050] 2) In boost mode: When the duty cycle of the 3rd switch (Q3) and the 7th switch (Q7) is less than 0.5, the duty cycle of the 4th switch (Q4) and the 8th switch (Q8) is fixed at 0.5; when the duty cycle of the 3rd switch (Q3) and the 7th switch (Q7) is greater than or equal to 0.5, the duty cycles of the 3rd switch (Q3), the 4th switch (Q4), the 7th switch (Q7) and the 8th switch (Q8) are the same.

[0051] Invention Effects

[0052] The bidirectional DC-DC converter according to the present invention enables DC bus voltage operation and inductor current equalization over a wide range of boost / buck voltage ratios, thereby further improving the voltage ratio and output power. Furthermore, the bidirectional DC-DC converter according to the present invention can achieve a maximum boost ratio of 39 times (duty cycle of 0.9) and a buck ratio of 0.0256 times (duty cycle of 0.1), and the highest power conversion efficiency can reach approximately 98%. Attached Figure Description

[0053]

【 Figure 1 Schematic diagram of a bidirectional DC-DC converter

[0054]

【 Figure 2 Circuit diagram of a bidirectional DC-DC converter

[0055]

【 Figure 3 Control block diagram of the drive circuit for a bidirectional DC-DC converter

[0056]

【 Figure 4 Switching operation diagram of the drive circuit of a bidirectional DC-DC converter in buck mode.

[0057]

【 Figure 5-1 In buck mode ( Figure 4 The circuit diagram for the bidirectional DC-DC converter shows the transitions between modes 1 and 8.

[0058]

【 Figure 5-2 In buck mode ( Figure 4 The circuit diagram for the bidirectional DC-DC converter shows the transitions between modes 1 and 6.

[0059]

【 Figure 6 Switching operation diagram of the drive circuit of a bidirectional DC-DC converter in boost mode.

[0060]

【 Figure 7-1 In boost mode ( Figure 6 The circuit diagram for the bidirectional DC-DC converter shows the transitions between modes 1 and 6.

[0061]

【 Figure 7-2 In boost mode ( Figure 6 The circuit diagram for the bidirectional DC-DC converter shows the transitions between modes 1 and 8.

[0062]

【 Figure 8-1 A schematic diagram of the drive signal and inductor current when the high-side voltage is 800V and the low-side voltage is 72V in buck mode (with the duty cycle of switches Q2 and Q6 less than 0.5).

[0063]

【 Figure 8-2 A schematic diagram of the drive signal and inductor current when the high-side voltage is 400V and the low-side voltage is 72V in buck mode (with the duty cycle of switches Q2 and Q6 greater than or equal to 0.5).

[0064]

【 Figure 8-3 A schematic diagram of the drive signal and inductor current when the high-side voltage is 400V and the low-side voltage is 72V in boost mode (with the duty cycle of switches Q3 and Q7 less than 0.5).

[0065]

【 Figure 8-4 A schematic diagram of the drive signal and inductor current when the high-side voltage is 800V and the low-side voltage is 72V in boost mode (with the duty cycle of switches Q3 and Q7 greater than or equal to 0.5).

[0066]

【 Figure 9-1 Bidirectional DC-DC converter buck mode (V c con ≤0.5, V H Simulation waveform at 800V

[0067]

【 Figure 9-2 Bidirectional DC-DC converter buck mode (V c co >0.5, V H Simulation waveform at 400V

[0068]

【 Figure 10-1 Bidirectional DC-DC converter boost mode (V d con <0.5, V H Simulation waveform at 400V

[0069]

【 Figure 10-2Bidirectional DC-DC converter boost mode (V d con ≥0.5, V H Simulation waveform at 800V

[0070]

【 Figure 11 Voltage ratio curves of bidirectional DC-DC converter in buck / boost modes

[0071]

【 Figure 12 [Graph of experimental drive signal versus experimental inductor current in buck mode]

[0072]

【 Figure 13 Measured efficiency curves of bidirectional DC-DC converter in buck / boost modes

[0073]

【 Figure 14 A diagram illustrating the configuration of a DC microgrid system connecting electric vehicles (EVs), etc. Detailed Implementation

[0074] Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the scope of the present invention is not limited to the following embodiments and illustrated examples, and various changes and modifications are possible.

[0075]

Example 1

[0076] Figure 1 A schematic diagram of the four-phase floating interleaved bidirectional DC-DC converter of the present invention is shown. As previously mentioned, in a DC microgrid system connected to an EV, the DC bus voltage is typically between 200V and 380V, while the EV battery voltage typically ranges from 400V to 800V, and the energy storage system (ESS) voltage is typically in the tens of volts range. The bidirectional DC-DC converter of the present invention serves as an interface between the low-voltage side ESS and the high-voltage side EV battery, enabling direct connection of the EV battery to the ESS without going through the DC microgrid bus. This design not only helps reduce power losses in the bidirectional DC-DC converter but also effectively suppresses voltage fluctuations in the DC microgrid.

[0077] Here, the ESS voltage V L This is called the low-voltage side voltage, or EV battery voltage V. H This is called the high-voltage side voltage, and it will come from V H To V L The power transfer is called buck mode, which will transfer power from V L To V H The power transmission in this mode is called boost mode.

[0078] Figure 2 The circuit structure of the four-phase floating interleaved bidirectional DC-DC converter of the present invention is shown. For example... Figure 2 As shown, the bidirectional DC-DC converter of this invention consists of a pair (two) of two-phase interleaved charge pump bidirectional DC-DC converters. The positive and negative terminals of the low-voltage side of each two-phase interleaved charge pump bidirectional DC-DC converter are connected in parallel to the low-voltage side DC bus, while one end of the high-voltage side of each DC-DC converter is connected to the positive and negative terminals of the high-voltage side DC bus, and the other end is in a floating state. The bidirectional DC-DC converter of this invention comprises active switches (Q1~Q4 and Q5~Q4). 8) Charge pump capacitor (C) 1B and C 2B Inductors (L1, L2 and L3, L4), low-voltage side filter capacitors (C) L ) and high-voltage side filter capacitor (C H1 and C H2 )constitute.

[0079] The DC-DC converter circuit connected to the high-side consists of the following components: two inductors (L1, L2) connected in parallel to the positive side of the low-voltage DC bus; an active switch (Q2) connected in series with inductor (L1); an active switch (Q1) connected between active switch (Q2) and the positive side of the high-voltage DC bus; an active switch (Q3) connected between inductor (L1) and the negative side of the low-voltage DC bus; an active switch (Q4) connected between inductor (L2) and the negative side of the low-voltage DC bus; and a high-voltage side filter capacitor (C) connected between the positive side of the high-voltage DC bus and the negative side of the low-voltage DC bus. H1 ); connected between the positive and negative sides of the low-voltage DC bus, and the high-voltage side filter capacitor (C) H1 The low-voltage side filter capacitor (C) is directly connected to its low potential. L ); and a charge pump capacitor (C) connected between the connection points of the active switches (Q1, Q2) and the connection points of the inductor (L2) and the active switch (Q4). 1B ).

[0080] In addition, the DC-DC converter circuit connected to the low-side consists of the following components: two inductors (L3, L4) connected in parallel to the negative side of the low-voltage DC bus; an active switch (Q6) connected in series with the inductor (L3); an active switch (Q5) connected between the active switch (Q6) and the negative side of the high-voltage DC bus; an active switch (Q7) connected between the inductor (L3) and the positive side of the low-voltage DC bus; an active switch (Q8) connected between the inductor (L4) and the positive side of the low-voltage DC bus; and a high-voltage side filter capacitor (C) connected between the negative side of the high-voltage DC bus and the positive side of the low-voltage DC bus. H2); and a charge pump capacitor (C) connected between the connection points of the active switches (Q5, Q6) and the connection points of the inductor (L4) and the active switch (Q8). 2B ).

[0081] The gate signals of the active switches (Q1~Q8) are controlled for high-speed turn-on / off via drive circuit 2. Drive circuit 2 is based on the synthesized value (i) of the four-phase currents of the inductors (L1~L4). LT The error amplification value between the active switch (Q1) and its reference value sets an upper limit limit on the duty cycle of the switching drive pulses of the active switches (Q4) and (Q8), and a lower limit limit on the duty cycle of the switching drive pulses of the active switches (Q5) and (Q1). Furthermore, this drive circuit 2 enables the active switches (Q1) and (Q5), (Q2) and (Q6), (Q3) and (Q7), and (Q4) and (Q8) to be driven with a phase difference of 90° from each other.

[0082] Drive circuit 2 adopts, for example Figure 3 The control logic shown is a closed-loop control method with asymmetric duty cycle limiting control (hereinafter referred to as DLC). An external voltage (low-voltage side voltage V) is used in the control. L and high voltage side voltage V H The drive circuit 2 detects the combined current of the four-phase inductor currents, compares it with a reference value, and then adjusts the current through a proportional control. The integral (PI) controller obtains the control output of the internal current loop. Next, through a limiting circuit, the duty cycle of the switching drive pulses acting on the active switches (Q1~Q8) is determined based on the input and output voltages in buck or boost mode. To amplify the error between the synthesized four-phase inductor current and its reference value, asymmetrical control of the duty cycle in charging and discharging modes is used to balance the four-phase inductor currents. Furthermore, by expanding the duty cycle range, a wider range of voltage fluctuations can be addressed.

[0083] Taking buck mode as an example, the control signal is compared with a triangular carrier wave to obtain the duty cycle signal. This duty cycle signal is then used by DLC1 to obtain the final duty cycle of the switch. Here, the duty cycle signal is directly used to control the duty cycle of the active switch. Furthermore, the active switches have sequential phase differences and operate under synchronous rectification conditions. The same control logic can also be applied to boost mode.

[0084] V o The baseline value is based on the action pattern in V o and V o,ref Switch between them. Lt,refIt is generated through PI control of voltage error. i is calculated by the PI controller. Lt,ref The value of the input current i Lt The error between (the combined value of the four-phase inductor current) is then used by the PI controller to determine the duty cycle of the switch in each mode. Here, V con From voltage The duty cycle control value of the switch is calculated from the current control loop; in addition, V c con It is the duty cycle control quantity of the switch in charging mode, while V d con This is the duty cycle control value for the switch in discharge mode. The mode selector is based on the low-voltage side voltage V. L and high voltage side voltage V H It generates switching drive pulse modes corresponding to buck and boost modes.

[0085] The driving circuit 2 enables the active switches (Q1) and (Q4), (Q2) and (Q3), (Q5) and (Q8), and (Q6) and (Q7) to conduct in a complementary manner.

[0086] (1) In buck mode, active switches (Q1, Q2) are the main switches of the DC-DC converter circuit connected to the high side, while active switches (Q5, Q6) are the main switches of the DC-DC converter circuit connected to the low side. There is a 180° phase difference between active switches (Q1) and (Q2), a 180° phase difference between active switches (Q5) and (Q6), and a 90° phase difference between active switches (Q1) and (Q5).

[0087] (2) In boost mode, active switches (Q3, Q4) are the main switches of the DC-DC converter circuit connected to the high side, while active switches (Q7, Q8) are the main switches of the DC-DC converter circuit connected to the low side. There is a 180° phase difference between active switches (Q3) and (Q4), a 180° phase difference between active switches (Q7) and (Q8), and a 90° phase difference between active switches (Q4) and (Q8).

[0088] Specifically, drive circuit 2 according to Figure 3 The control logic action is shown. The duty cycle (D) of the switching drive pulse of the active switch (Q1) is... Q1 The duty cycle (D) of the switching drive pulse of the active switch (Q4) Q4 The duty cycle (D) of the switching drive pulse of the active switch (Q5) Q5) and the duty cycle (D) of the switching drive pulse of the active switch (Q8). Q8 The same applies in both boost and buck modes, and each satisfies 0 < D. Q1 ≤ 0.5, 0.5 ≤ D Q4 < 1、0 < D Q5 ≤ 0.5, 0.5 ≤ D Q8 <1.

[0089] In addition, the duty cycle (D) of the switching drive pulse of the active switch (Q2) Q2 The duty cycle of the switching drive pulse of the active switch (Q3) (D) Q3 The duty cycle of the switching drive pulse of the active switch (Q6) (D) Q6 ) and the duty cycle of the switching drive pulse of the active switch (Q7) (D Q7 The same applies in both boost and buck modes, and each satisfies 0 < D. Q1 < 1、0 < D Q3 < 1, 0 <D Q6 < 1、0 < D Q7 < 1.

[0090] The sum of the duty cycles of active switch (Q1) and active switch (Q4), active switch (Q2) and active switch (Q3), active switch (Q5) and active switch (Q8), and active switch (Q6) and active switch (Q7) are all 1.

[0091] (1) In step-down mode, when the duty cycle of active switch (Q2) and active switch (Q6) is less than 0.5, the duty cycles of active switch (Q1), active switch (Q2), active switch (Q5) and active switch (Q6) are the same; if the duty cycle of active switch (Q2) and active switch (Q6) is greater than or equal to 0.5, the duty cycle of active switch (Q1) and active switch (Q5) is fixed at 0.5.

[0092] (2) In boost mode, when the duty cycle of active switch (Q3) and active switch (Q7) is less than 0.5, the duty cycle of active switch (Q4) and active switch (Q8) is fixed at 0.5; when the duty cycle of active switch (Q3) and active switch (Q7) is greater than or equal to 0.5, the duty cycles of active switch (Q3), active switch (Q4), active switch (Q7) and active switch (Q8) are the same.

[0093] Figure 4 Figures (1) and (2) show the switching waveforms of the active switches (Q1, Q2, Q5, Q6) in buck mode. Figure 4 (1) indicates the case where the duty cycle of the active switches (Q2, Q6) is greater than or equal to 0.5, while Figure 4 (2) indicates that the duty cycle of the active switches (Q2, Q6) is less than 0.5. As mentioned above, in Figure 4 In (1), the duty cycle of the active switches (Q1, Q5) is fixed at 0.5; while Figure 4 In (2), the duty cycles of the active switches (Q1, Q2, Q5, Q6) are all the same.

[0094] like Figure 4 (1) shows that when the duty cycle of the active switches (Q2, Q6) is greater than or equal to 0.5, the switching period T of the bidirectional DC-DC converter is... c The memory has six buck modes, from mode 1 to mode 6. And as... Figure 4 As shown in (2), when the duty cycle of the active switches (Q2, Q6) is less than 0.5, the switching period T of the bidirectional DC-DC converter is... c There are 8 voltage reduction modes, from mode 1 to mode 8.

[0095] Figure 5-1 The buck mode is shown. Figure 4 The current flow of the bidirectional DC-DC converter circuit corresponding to (1) is shown to be... Figure 4 The switching period T shown in (1) c Current flow direction among the six buck modes (internal modes 1 to 6).

[0096] Figure 5-2 When the buck mode is shown ( Figure 4 The conversion diagram of the bidirectional DC-DC converter circuit corresponding to (2)) between buck modes 1 and 8 shows that Figure 4 The switching period T shown in (2) c The current flow direction between the eight internal modes 1 to 8. In the diagram, the "×" symbol indicates that the switch is in the OFF state.

[0097] Figure 6 Figures (1) and (2) show the switching waveforms of the active switches (Q3, Q4, Q7, Q8) in boost mode, respectively. Figure 6 (1) indicates the case where the duty cycle of the active switches (Q3, Q7) is less than 0.5, while Figure 6 (2) indicates the case where the duty cycle of the active switches (Q3, Q7) is greater than or equal to 0.5. As mentioned above, in Figure 6 In (1), the duty cycle of the active switches (Q4, Q8) is fixed at 0.5; while Figure 6 In (2), the duty cycles of the active switches (Q3, Q4, Q7, Q8) are all the same.

[0098] when Figure 6 (1) When the duty cycle of the active switches (Q3, Q7) is less than 0.5, the switching period T of the bidirectional DC-DC converter is... c The memory has 6 boost modes, from mode 1 to mode 6; and when Figure 6 (2) When the duty cycle of the active switches (Q3, Q7) is greater than or equal to 0.5, the switching period T c The memory has 8 boost modes, from mode 1 to mode 8.

[0099] Figure 7-1 When the buck mode is shown ( Figure 6 The conversion diagram of the bidirectional DC-DC converter circuit corresponding to (1)) between buck modes 1 and 6 presents... Figure 6 The switching period T shown in (1) c The current flow in six modes, from mode 1 to mode 6.

[0100] Figure 7-2 When boost mode is shown ( Figure 6 The conversion diagram of the bidirectional DC-DC converter circuit corresponding to (2)) between boost modes 1 and 8 shows that Figure 6 The switching period T shown in (2) c The diagram shows the current flow in eight modes, from mode 1 to mode 8. The "×" symbol in the diagram indicates that the switch is in the OFF state.

[0101] Figure 8-1 (1) The theoretical drive signals of each active switch (Q1, Q2, Q5, Q6) are shown in buck mode (high-side voltage 800V, low-side voltage 72V) when the duty cycle of the active switches (Q2, Q6) is less than 0.5. Since each active switch (Q1, Q2, Q5, Q6) has the same duty cycle, and there is a 180° phase difference between active switches (Q1, Q2), a 90° phase difference between active switches (Q1, Q5), and a 180° phase difference between active switches (Q5, Q6), there is a 270° phase difference between active switches (Q1, Q6). Figure 8-1 (1) Under the condition that the duty cycle of the active switches (Q2, Q6) shown is less than 0.5, the switching period T of the bidirectional DC-DC converter is... c There are eight modes, from mode 1 to mode 8, within the system. Furthermore, Figure 8-1 (2) shows Figure 8-1 (1) The inductor current (i) corresponding to each active switch (Q1, Q2, Q5, Q6) during the switching operation period L1 i L2 i L3 i L4 Waveform.

[0102] Figure 8-2 (1) The theoretical drive signals of each active switch (Q1, Q2, Q5, Q6) are shown in buck mode (high voltage side voltage is 400V, low voltage side voltage is 72V) when the duty cycle of the active switches (Q2, Q6) is greater than or equal to 0.5. The duty cycle of the active switches (Q1, Q5) is fixed at 0.5, and there is a 180° phase difference between active switches (Q1, Q2), a 90° phase difference between active switches (Q1, Q5), and a 180° phase difference between active switches (Q5, Q6). Therefore, there is a 270° phase difference between the active switches (Q1, Q6). Figure 8-2 (1) When the duty cycle of the active switches (Q2, Q6) shown is greater than or equal to 0.5, the switching period T of the bidirectional DC-DC converter is... c The memory has six modes, from mode 1 to mode 6. In addition, Figure 8-2 (2) shows Figure 8-2 (1) The corresponding inductor current (i) of each active switch (Q1, Q2, Q5, Q6) during the switching operation process L1 i L2 i L3 i L4 Waveform.

[0103] Figure 8-3 (1) The theoretical drive signals of each active switch (Q3, Q4, Q7, Q8) are shown in boost mode (high voltage side voltage is 400V, low voltage side voltage is 72V) when the duty cycle of the active switches (Q3, Q7) is less than 0.5. The duty cycle of the active switches (Q4, Q8) is fixed at 0.5, and there is a 180° phase difference between the active switches (Q4, Q3), a 90° phase difference between the active switches (Q4, Q8), and a 180° phase difference between the active switches (Q8, Q7). Therefore, there is a 270° phase difference between the active switches (Q4, Q7). Figure 8-3 (1) When the duty cycle of the active switches (Q3, Q7) shown is less than 0.5, the switching period T of the bidirectional DC-DC converter is... c The memory has six modes, from mode 1 to mode 6. In addition, Figure 8-3 (2) shows Figure 8-3 (1) The corresponding inductor current (i) of each active switch (Q1, Q2, Q5, Q6) during the switching operation process L1 i L2 i L3 i L4 Waveform.

[0104] Figure 8-4(1) The theoretical drive signals of each active switch (Q3, Q4, Q7, Q8) are shown in boost mode (high voltage side voltage 800V, low voltage side voltage 72V) when the duty cycle of the active switches (Q3, Q7) is greater than or equal to 0.5. Since each active switch (Q3, Q4, Q7, Q8) has the same duty cycle, and there is a 180° phase difference between active switches (Q4, Q3), a 90° phase difference between active switches (Q4, Q8), and a 180° phase difference between active switches (Q8, Q7), there is a 270° phase difference between active switches (Q4, Q7). Figure 8-4 (1) When the duty cycle of the active switches (Q3, Q7) shown is greater than or equal to 0.5, the switching period T of the bidirectional DC-DC converter is... c The memory has eight modes, from mode 1 to mode 8. In addition, Figure 8-4 (2) shows Figure 8-4 (1) The inductor current (i) corresponding to each active switch (Q3, Q4, Q7, Q8) during the switching operation period L1 i L2 i L3 i L4 Waveform.

[0105] The performance of the bidirectional DC-DC converter of this invention is explained through experimental verification results based on a 1kW-50kHz prototype. The main circuit parameters are shown in Table 1. Switches Q1 to Q8 are implemented using active switching devices SiC-MOSFETs (model: IMW65R027M1H, 650V, 47A, 27mΩ). Furthermore, all self-turn-off switching devices such as Si-MOSFETs and Si-IGBTs can be used as active switches. Based on the specifications and parameters in Table 1, performance tests were conducted on the bidirectional DC-DC converter of this invention with a rated power of 1kW to verify the wide voltage ratio characteristic between the adjustable DC bus voltage (400-800V) and the fixed low-voltage side voltage (72V). In buck mode, Figure 9-1 The values ​​displayed are 800V input voltage, 72V output voltage, and V. con The waveforms of gate drive, input / output voltage, and inductor current when the phase difference is less than 0.5. This shows that the active switches (Q1, Q5, Q2, Q6) have the same duty cycle and a 90° phase difference between them. However, DLC control (buck mode) is not activated at this time, and all inductor currents automatically maintain a 90° phase difference and almost identical average current.

[0106] Table 1

[0107]

[0108] on the other hand, Figure 9-2The figures show the conditions when the input voltage is 400V, the output voltage is 72V, and V... con The waveforms of the gate drive signal, input / output voltage, and inductor current are shown when the voltage is greater than or equal to 0.5. Although the switching actions of the active switches (Q1, Q5, Q2, Q6) have a 90° phase difference, their duty cycles are different. Under DLC control (buck mode), the duty cycle D1 is limited to 0.5. Therefore, it can be confirmed that the gate drive pulse control in the bidirectional DC-DC converter of this invention has the effect of achieving average inductor current balance.

[0109] Even in boost mode, such as Figure 10-1 and Figure 10-2 As shown, DLC control (boost mode) also exhibits the same result.

[0110] Next, Figure 11 The voltage conversion ratio (VCR) characteristics of IBDC, ICPBDC, and the bidirectional DC-DC converter (4F-ICPBDC) of this invention are shown in buck and boost modes. Compared with IBDC and ICPBDC, the bidirectional DC-DC converter (4F-ICPBDC) of this invention exhibits... Figure 11 (1) The buck mode shown has a higher buck ratio, in Figure 11 (2) The boost mode shown exhibits a higher boost ratio. Specifically, the values ​​marked with "*" in the experimental results are the obtained data. The maximum boost ratio reaches 39 times (at a duty cycle of 0.9), and the maximum buck ratio reaches 0.0256 times (at a duty cycle of 0.1).

[0111] The high-voltage side voltage V of the bidirectional DC-DC converter (4F-ICPBDC) of this invention H This refers to the voltage (V) of the high-voltage side filter capacitors of each DC-DC converter. H1 V H2 ) and low-voltage side voltage V L Formed by superposition. Specifically, satisfying V H = V H1 + V H2 -V L Furthermore, when the duty cycle of the switch in the bidirectional DC-DC converter (4F-ICPBDC) is set to D (buck mode: D...), c Boost mode: D d When ), the high-voltage side voltage V H With low-voltage side voltage V L The voltage ratio satisfies the following relationship: In buck mode, V L / VH =D c / (4 - D c In boost mode, V H / V L = (3 + D d ) / (1 - D d For the derivation of the voltage ratio, please refer to the aforementioned non-patent literature 1.

[0112] then, Figure 12 The diagram shows the gate signal of the switch and the average current of the inductors (L1, L2, L3, L4) measured in the circuit of the prototype. Over one switching cycle T... s During this period, the on-time of switches (Q1, Q5) is limited to 0.5 T during the on-time of the switches that bias the charge pump capacitor. s The conduction time of the other set of switches (Q2, Q6) is 0.61 T. s Furthermore, each switch is driven sequentially with a predetermined phase difference. Figure 12 (1) is the experimental driving signal (the gate signal of switches Q1, Q2, Q5, and Q6). Figure 12 (2) is the experimental inductor current (i L1 i L2 i L3 i L4 Compared to the inductor current obtained based on the theoretical drive signal tail in Figure 8-2 above, as... Figure 12 As shown, the inductor current waveform measured in this experiment is consistent with the inductor current waveform when the high-side voltage is 400V and the low-side voltage is 72V in buck mode, and the duty cycles of switches (Q2, Q6) are both greater than or equal to 0.5. Therefore, it can be confirmed through the prototype that the average inductor current in the bidirectional DC-DC converter of this invention remains essentially balanced.

[0113] Furthermore, similarly, the waveform of the inductor current is consistent with that of the switches (Q3, Q7) when the duty cycle is less than 0.5, which is the case when the high-side voltage is 400V and the low-side voltage is 72V in boost mode. Therefore, it can be confirmed through a prototype that the average inductor current can remain essentially balanced in the bidirectional DC-DC converter of this invention.

[0114] The actual power conversion efficiency of the bidirectional DC-DC converter (4F-ICPBDC) of the present invention is evaluated by an open-loop control method.

[0115] like Figure 13As shown in (1), in the measured efficiency of the prototype in buck mode, the maximum power conversion efficiency of the converter reaches 98.3% and 96.9% when the input voltage is 400V and 800V respectively, and the rated output (72V) is 100V and 800V respectively. On the other hand, in the measured efficiency of the prototype in boost mode, as shown in (1), the maximum power conversion efficiency of the converter reaches 98.3% and 96.9% when the input voltage is 400V and 800V respectively, and the rated output (72V) is 800V and 800V respectively. Figure 13 As shown in (2), the maximum power conversion efficiency reaches 97.6% and 96.9% when the input voltage is 72V and the output voltage is 400V and 800V, respectively. In addition, when the output power is less than 300W, the efficiency is expected to decrease due to the conduction loss of the circuit components.

[0116] Therefore, by implementing DLC ​​control in the bidirectional DC-DC converter (4F-ICPBDC), the average inductor current can be kept balanced across the entire duty cycle range, whether in buck or boost mode, and high boost ratio and high buck ratio characteristics are theoretically achieved, covering the entire duty cycle range.

[0117] Industrial application

[0118] This invention is applicable to DC power grid systems connected to electric vehicles (EVs) or on-board power systems (electric vehicles, trams) that require bidirectional DC power conversion.

[0119] Explanation of symbols in the diagram

[0120] 1. Bidirectional DC-DC converter

[0121] 2. Drive Circuit

Claims

1. A bidirectional DC-DC converter, characterized in that, It consists of a pair of two-phase interleaved charge pump bidirectional DC-DC converters. The positive and negative terminals of the low-voltage side of each of the aforementioned DC-DC converters are connected in parallel to the low-voltage side DC bus. One end of the high-voltage side of each DC-DC converter is connected to the positive and negative terminals of the high-voltage side DC bus, while the other end is in a floating state.

2. The bidirectional DC-DC converter as described in claim 1, characterized in that, The high-voltage side voltage of the DC-DC converter is the voltage formed by superimposing the high-voltage side filter capacitor voltage of each DC-DC converter with the low-voltage side voltage of the DC-DC converter. High voltage side voltage V H With low-voltage side voltage V L The voltage ratio between them, in buck mode, satisfies V L / V H =D / (4-D), which satisfies V in boost mode. H / V L =(3+D) / (1-D), where D represents the duty cycle of the switch in the DC-DC converter.

3. The bidirectional DC-DC converter as described in claim 2, characterized in that, In a pair of DC-DC converters, based on the amplified error between the combined value of the four-phase inductor current and the reference value, an asymmetrical upper or lower limit is set for the duty cycle of the drive pulses of the switches that are the controlled objects, respectively, in boost mode and buck mode, and switching control is performed.

4. The bidirectional DC-DC converter as described in claim 3, comprising: The DC-DC converter circuit connected to the high side includes: The first and second inductors (L1, L2) are connected in parallel on the positive side of the low-voltage DC bus. The second switch (Q2) is connected in series with the first inductor (L1). The first switch (Q1) is connected between the second switch (Q2) and the positive side of the high-voltage DC bus. The third switch (Q3) is connected between the first inductor (L1) and the negative terminal of the low-voltage DC bus. The fourth switch (Q4) is connected between the second inductor (L2) and the negative terminal of the low-voltage DC bus. The first high-voltage side filter capacitor (C) is connected between the positive side of the high-voltage DC bus and the negative side of the low-voltage DC bus. H1 ), The first high-voltage side filter capacitor (C) is connected between the positive and negative sides of the low-voltage DC bus. H1 The low-voltage side filter capacitor (C) is directly connected to its low-potential terminal. L ), And the first charge pump capacitor (C) connected between the connection points of the first and second switches (Q1, Q2) and the connection point of the second inductor (L2) and the fourth switch (Q4). 1B ); and The DC-DC converter circuit connected to the low side includes: The third and fourth inductors (L3, L4) are connected in parallel on the negative side of the low-voltage DC bus. The sixth switch (Q6) is connected in series with the third inductor (L3). The fifth switch (Q5) is connected between the sixth switch (Q6) and the negative side of the high-voltage DC bus. The seventh switch (Q7) is connected between the third inductor (L3) and the positive terminal of the low-voltage DC bus. The 8th switch (Q8) is connected between the 4th inductor (L4) and the positive side of the low-voltage DC bus. The second high-voltage side filter capacitor (C) is connected between the negative side of the high-voltage DC bus and the positive side of the low-voltage DC bus. H2 ), The second charge pump capacitor (C) is connected between the connection point of switches 5 and 6 (Q5, Q6) and the connection point of inductor 4 (L4) and switch 8 (Q8). 2B );as well as The drive circuit used to control switches 1 through 8, wherein, The driving circuit sets an upper limit on the duty cycle of the switching drive pulses for the first switch (Q1) and the fifth switch (Q5), and a lower limit on the duty cycle of the switching drive pulses for the fourth switch (Q4) and the eighth switch (Q8), respectively, to compensate for the error amplification between the combined value of the four-phase currents of the first inductor (L1) to the fourth inductor (L4) and the reference value. The first switch (Q1) and the fifth switch (Q5), the second switch (Q2) and the sixth switch (Q6), the third switch (Q3) and the seventh switch (Q7), and the fourth switch (Q4) and the eighth switch (Q8) are driven with a phase difference of 90° between them.

5. The bidirectional DC-DC converter as described in claim 4, characterized in that, The driving circuit enables the first switch (Q1) and the fourth switch (Q4), the second switch (Q2) and the third switch (Q3), the fifth switch (Q5) and the eighth switch (Q8), and the sixth switch (Q6) and the seventh switch (Q7) to be complementaryly turned on; In buck mode Switches 1 and 2 (Q1, Q2) are the main switches of the DC-DC converter circuit connected to the high side, while switches 5 and 6 (Q5, Q6) are the main switches of the DC-DC converter circuit connected to the low side. There is a 180° phase difference between the first switch (Q1) and the second switch (Q2). There is a 180° phase difference between switch 5 (Q5) and switch 6 (Q6). There is a 90° phase difference between the first switch (Q1) and the fifth switch (Q5); In boost mode Switches 3 and 4 (Q3, Q4) are the main switches of the DC-DC converter circuit connected on the high side, while switches 7 and 8 (Q7, Q8) are the main switches of the DC-DC converter circuit connected on the low side. There is a 180° phase difference between the third switch (Q3) and the fourth switch (Q4). There is a 180° phase difference between switch 7 (Q7) and switch 8 (Q8). There is a 90° phase difference between the 4th switch (Q4) and the 8th switch (Q8).

6. The bidirectional DC-DC converter as described in claim 5, characterized in that, The duty cycle (D) of the switching drive pulse of the first switch (Q1) Q1 The duty cycle (D) of the switching drive pulse of the fourth switch (Q4) Q4 The duty cycle (D) of the switching drive pulse of the 5th switch (Q5) Q5 ) and the duty cycle (D) of the switching drive pulse of the 8th switch (Q8) Q8 The voltage remains consistent in both boost and buck modes, and each satisfies 0 < D. Q1 ≦0.5、0.5≦D Q4 <1、0 <D Q5 ≦0.5、0.5≦D Q8 < 1; The duty cycle (D) of the switching drive pulse of the second switch (Q2) Q2 The duty cycle (D) of the switching drive pulse of the third switch (Q3) Q3 The duty cycle (D) of the switching drive pulse of the 6th switch (Q6) Q6 ) and the duty cycle (D) of the switching drive pulse of the 7th switch (Q7) Q7 The voltage remains consistent in both boost and buck modes, and each satisfies 0 < D. Q1 <1、0 <D Q3 <1、0 <D Q6 <1、0 <D Q7 <1.

7. The bidirectional DC-DC converter as described in claim 6, wherein, The driving circuit satisfies: The sum of the duty cycles of the first switch (Q1) and the fourth switch (Q4), the sum of the duty cycles of the second switch (Q2) and the third switch (Q3), the sum of the duty cycles of the fifth switch (Q5) and the eighth switch (Q8), and the sum of the duty cycles of the sixth switch (Q6) and the seventh switch (Q7) are all 1. In step-down mode, when the duty cycle of the second switch (Q2) and the sixth switch (Q6) is less than 0.5, the duty cycles of the first switch (Q1), the second switch (Q2), the fifth switch (Q5), and the sixth switch (Q6) are the same; when the duty cycle of the second switch (Q2) and the sixth switch (Q6) is greater than or equal to 0.5, the duty cycle of the first switch (Q1) and the fifth switch (Q5) is fixed at 0.

5. In boost mode, when the duty cycle of the 3rd switch (Q3) and the 7th switch (Q7) is less than 0.5, the duty cycle of the 4th switch (Q4) and the 8th switch (Q8) is fixed at 0.5; when the duty cycle of the 3rd switch (Q3) and the 7th switch (Q7) is greater than or equal to 0.5, the duty cycles of the 3rd switch (Q3), the 4th switch (Q4), the 7th switch (Q7), and the 8th switch (Q8) are the same.

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