Power conversion device

Abstract

The invention provides a power conversion device, and the device comprises a power converter which comprises a bidirectional AC / DC converter, a DC bus, and a bidirectional DC / DC converter, the first controller is configured to execute the following steps: a first arithmetic unit receives an alternating-current voltage sampling signal from the alternating-current end of the bidirectional AC / DC converter and an alternating-current voltage reference signal, and outputs an alternating-current voltage difference signal; the first compensation unit receives the alternating-current voltage difference signal and outputs a compensated alternating-current voltage difference signal; the amplitude limiting unit receives the compensated AC voltage difference signal and a bus voltage sampling signal from a DC bus, and outputs a current reference signal; the second arithmetic unit receives an alternating current sampling signal and a current reference signal from the alternating current end and outputs an alternating current difference signal; the second compensation unit receives the alternating current difference signal and outputs a compensated alternating current difference signal; the first modulation unit receives the compensated alternating current difference signal and outputs a first switch control signal.

Description

Technical Field

[0001] This application relates to the field of power supplies, and in particular to power conversion devices. Background Technology

[0002] Two-stage power converters, including cascaded bidirectional AC / DC converters, DC buses, and bidirectional DC / DC converters, are used in many applications, such as electric vehicles. In these applications, the DC terminal of the power converter is used to connect to the high-voltage power battery, and the AC terminal is used to connect to the AC power grid or AC loads.

[0003] When the DC terminal of the power converter is connected to a load and requires power, the power converter is controlled to operate in rectification mode, converting AC to DC. When the AC terminal of the power converter is connected to an AC load and requires power, the power converter is controlled to operate in inverter mode, converting DC to AC.

[0004] In practical applications, it is desirable for power converters to be stable and reliable during operation, and for their size to be as small as possible, in order to meet the current market demand for high power density. Application content

[0005] This application discloses a power conversion device, comprising: a power converter including a cascaded bidirectional AC / DC converter, a DC bus, and a bidirectional DC / DC converter; a first controller, configured to execute the following when the power converter operates in inverter mode: a first arithmetic unit receives an AC voltage sampling signal from the AC terminal of the bidirectional AC / DC converter and an AC voltage reference signal, and outputs an AC voltage difference signal; a first compensation unit receives the AC voltage difference signal and outputs a compensated AC voltage difference signal; a limiting unit receives the compensated AC voltage difference signal and a bus voltage sampling signal from the DC bus, and outputs a current reference signal; a second arithmetic unit receives an AC current sampling signal from the AC terminal and the current reference signal, and outputs an AC current difference signal; a second compensation unit receives the AC current difference signal and outputs a compensated AC current difference signal; and a first modulation unit receives the compensated AC current difference signal and outputs a first switching control signal controlling the switching transistors within the bidirectional AC / DC converter.

[0006] Furthermore, it also includes a second controller. When the power converter operates in inverter mode, the second controller is configured to execute: a third arithmetic unit receives a bus voltage sampling signal and a bus voltage reference signal from the DC bus, and outputs a bus voltage difference signal; a third compensation unit receives the bus voltage difference signal and outputs a compensated bus voltage difference signal; and a second modulation unit receives the compensated bus voltage difference signal and outputs a second switching control signal to control the switching transistors within the DC / DC converter.

[0007] Furthermore, when the bus voltage sampling signal decreases, the current reference signal output by the limiting single unit also decreases to ensure the stability of the DC bus voltage.

[0008] Furthermore, when the bus voltage sampling signal increases, the current reference signal output by the limiting single unit also increases to ensure the stability of the DC bus voltage.

[0009] Furthermore, the bidirectional AC / DC converter is a PFC converter.

[0010] Furthermore, the bidirectional AC / DC converter is either a single-phase converter or a three-phase converter.

[0011] Furthermore, the bidirectional DC / DC converter is an LLC resonant converter.

[0012] Furthermore, when the power converter operates in rectification mode that converts AC power to DC power, the first controller is configured to output a first switching control signal to control the switching transistors within the bidirectional AC / DC converter based on AC voltage sampling signals and AC current sampling signals from the AC terminal of the bidirectional AC / DC converter, and bus voltage sampling signals from the DC bus.

[0013] Furthermore, the second controller is configured to output a second switching control signal to control the switching transistors within the bidirectional DC / DC converter based on voltage and current sampling signals from the DC output terminal of the bidirectional DC / DC converter and bus voltage sampling signals from the DC bus.

[0014] The features and technical advantages of this disclosure have been outlined quite extensively above to facilitate a better understanding of the detailed description that follows. Additional features and advantages of this disclosure, which form the subject matter of the claims, will be described below. Those skilled in the art will understand that the disclosed concepts and specific embodiments can be readily used as the basis for modifying or designing other structures or processes for achieving the same purpose as this disclosure. Those skilled in the art will also recognize that such equivalent structures do not depart from the spirit and scope of this disclosure as set forth in the appended claims. Attached Figure Description

[0015] Figure 1 A schematic diagram of a power conversion device according to an embodiment of this application is shown; Figure 2 A block diagram of a first controller according to an embodiment of this application is shown; Figure 3 A block diagram of a second controller according to an embodiment of this application is shown. Detailed Implementation

[0016] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0017] One embodiment of this application provides a power conversion device. For details, please refer to... Figure 1 The diagram shown is a schematic representation of a power conversion device according to an embodiment of this application. Please refer to it in conjunction with... Figure 2 The block diagram of the first controller according to an embodiment of this application shown herein includes a power conversion device comprising: The power converter includes a cascaded bidirectional AC / DC converter 110, a DC bus Cbus, and a bidirectional DC / DC converter 120. The first controller 210, when the power converter is operating in inverter mode, is configured to perform: The first arithmetic unit 211 receives an AC voltage sampling signal uac and an AC voltage reference signal Uacref from the AC terminal of the bidirectional AC / DC converter 110, and outputs an AC voltage difference signal Uac_d. The first compensation unit 212 receives the AC voltage difference signal Uac_d and outputs the compensated AC voltage difference signal Uac_r; The limiting unit 213 receives the compensated AC voltage difference signal Uac_r and the bus voltage sampling signal ubus from the DC bus, and outputs the current reference signal iLref; The second processing unit 214 receives the AC current sampling signal iL and the current reference signal iLref from the AC terminal, and outputs the AC current difference signal iL_d. The second compensation unit 215 receives the AC current difference signal iL_d and outputs the compensated AC current difference signal iL_r. The first modulation unit 216 receives the compensated AC current difference signal iL_r and outputs a first switching control signal to control the switching transistors inside the bidirectional AC / DC converter 110.

[0018] Please refer to the following: Figure 1 The bidirectional AC / DC converter 110 is a PFC converter. The bidirectional DC / DC converter 120 is an LLC resonant converter. Of course, this application does not limit the specific structure of the bidirectional AC / DC converter 110 and the bidirectional DC / DC converter 120. In actual implementation, any converter capable of bidirectional conversion between AC and DC can be used as the bidirectional AC / DC converter 110 of this application, and any converter capable of bidirectional conversion between DC and DC can be used as the bidirectional DC / DC converter 120 of this application.

[0019] Specifically, the bidirectional AC / DC converter 110 includes a first switching arm formed by a first switch S1 and a second switch S2 connected in series, a second switching arm formed by a third switch S3 and a fourth switch S4 connected in series, a first inductor L1, and a first capacitor C1. The first and second switching arms are connected in parallel, and their ends form the DC terminal of the bidirectional AC / DC converter 110. The two ends of the first and second switching arms form the AC terminal of the bidirectional AC / DC converter 110, i.e., the AC terminal of the power converter. Furthermore, the first inductor L1 is connected between one end of the first capacitor C1 and the common node A of the first switching arm or the common node B of the second switching arm. Figure 1 As shown, the first inductor L1 is connected between the first terminal of the first capacitor C1 and the common node A of the first switch bridge arm.

[0020] like Figure 1 As shown, the DC bus Cbus is connected in parallel to the DC terminal of the bidirectional AC / DC converter 110.

[0021] Specifically, the bidirectional DC / DC converter 120 includes a cascaded first switching unit, a resonant cavity, a transformer T, a second switching unit, and a second capacitor C2. The first switching unit includes a third switching arm formed by the series connection of the fifth switch S5 and the sixth switch S6, and a fourth switching arm formed by the series connection of the seventh switch S7 and the eighth switch S8. The third and fourth switching arms are connected in parallel, and their parallel connection forms the first DC terminal of the bidirectional DC / DC converter 120. The DC bus Cbus is also connected in parallel to the first DC terminal of the bidirectional DC / DC converter 120. The resonant cavity is connected between the common node C of the third switching arm or the common node D of the fourth switching arm and the primary winding Lp of the transformer T. Figure 1As shown, the resonant cavity is connected between the common node C of the third switching bridge arm and the primary winding Lp of the transformer T. Specifically, the resonant cavity includes a resonant capacitor Cr and a resonant inductor Lr connected in series. The second switching unit includes a fifth switching bridge arm formed by the series connection of the ninth switch S9 and the tenth switch S10, and a sixth switching bridge arm formed by the series connection of the eleventh switch S11 and the twelfth switch S12. The fifth and sixth switching bridge arms are connected in parallel. The second capacitor C2 is connected in parallel with the fifth and sixth switching bridge arms. The two ends of the second capacitor C2 form the second DC terminal of the bidirectional DC / DC converter 120.

[0022] When the power converter operates in rectification mode, which converts AC to DC, it converts the AC VAC at the AC terminal to DC VDC. When the power converter operates in inverter mode, which converts DC to AC, it converts the DC VDC at the second DC terminal to AC VAC at the AC terminal.

[0023] In practical applications, the first switch S1 to the twelfth switch S12 can be a MOSFET, a bipolar junction transistor, a superjunction transistor, an insulated gate bipolar transistor, a gallium nitride-based power device, and / or similar devices. Any device in the industry that can receive a switching control signal to turn on or off is acceptable.

[0024] In practical applications, the first switching unit and the second switching unit can be as follows: Figure 1 The full-bridge switching units shown can also all be half-bridge switching units, or one of them can be a half-bridge switching unit and the other can be a full-bridge switching unit. This application does not limit their specific structure.

[0025] like Figure 1 As shown, the bidirectional AC / DC converter 110 is a single-phase converter. In practical applications, it can also be a three-phase converter. That is, the bidirectional AC / DC converter 110 also includes another switch arm connected in parallel with the first switch arm and the second switch arm. This switch arm also includes two switch tubes connected in series (not shown in the figure). In this case, the AC load connected to the AC terminal can be a three-phase AC load.

[0026] In practical applications, when the power converter operates in inverter mode, in order to ensure the normal operation of the system, the bidirectional DC / DC converter is controlled by the second controller to ensure the DC bus voltage is stable, so as to provide a stable power supply for the bidirectional AC / DC converter. The first controller controls the bidirectional AC / DC converter to supply power to the AC load at the AC end. That is, the bidirectional AC / DC converter and the bidirectional DC / DC converter are controlled independently.

[0027] However, in practical applications, the AC load may change abruptly, such as sudden loading, unloading, or load shedding. That is, the power required by the AC load may suddenly increase, decrease, or drop to zero. In this case, the energy drawn by the bidirectional AC / DC converter 110 from the DC bus Cbus will also suddenly increase, decrease, or drop to zero. However, as mentioned above, the bidirectional AC / DC converter 110 and the bidirectional DC / DC converter 120 are controlled independently. Therefore, the bidirectional DC / DC converter 120 may not be able to respond to the sudden changes in the load in time so that the DC bus Cbus can provide the change in the energy drawn by the bidirectional AC / DC converter 110. This may cause the load to fail to work normally and also cause large fluctuations in the DC bus Cbus voltage, such as undervoltage or overvoltage problems, resulting in unstable operating conditions such as shutdown of the power conversion device.

[0028] Of course, in practical applications, the DC bus Cbus can be made large enough to ensure that the DC bus Cbus voltage remains stable when the AC load fluctuates. However, this greatly increases the size of the DC bus Cbus and the power conversion device, which contradicts the current market's pursuit of high power density.

[0029] Please refer to the following: Figure 1 and Figure 2 In the control loop of the bidirectional AC / DC converter 110, a DC bus Cbus voltage feedforward is added. The current reference signal iLref of the current loop of the bidirectional AC / DC converter 110 is controlled by limiting the DC bus Cbus voltage, thereby controlling the power drawn by the AC load from the DC bus Cbus. This ensures that the load can work normally and also provides the bidirectional DC / DC converter 120 with time to stabilize the DC bus Cbus voltage through the second controller in response to changes in the DC bus Cbus voltage.

[0030] Specifically, when the DC bus Cbus voltage decreases (e.g., less than the rated value, less than the set value, and / or continues to decrease), it may be due to a sudden loading of the AC load, i.e., a sudden increase in the power required by the AC load. In this case, the current reference signal iLref of the current loop can be reduced, i.e., the AC current output at the AC terminal of the bidirectional AC / DC converter 110 can be reduced, or the power consumed by the AC load can be reduced. This avoids a sudden drop in the DC bus Cbus voltage and ensures the stability of the DC bus Cbus voltage, so as to avoid the power conversion device from shutting down directly. Instead, it provides the bidirectional DC / DC converter 120 with time to raise the DC bus Cbus voltage in response to the sudden drop in the DC bus Cbus voltage.

[0031] Similarly, when the DC bus Cbus voltage increases (e.g., larger than the rated value, greater than the set value, and / or continues to decrease), it may be due to a sudden reduction or dumping of the AC load, i.e., a sudden decrease in the power required by the AC load. In this case, the current reference signal iLref of the current loop can be increased, i.e., the AC circuit output of the AC terminal of the bidirectional AC / DC converter 110 can be increased, or the power consumed by the AC load can be increased. This avoids a sudden rise in the DC bus Cbus voltage and ensures the stability of the DC bus Cbus voltage, so as to avoid the power conversion device from shutting down directly. Instead, it provides the bidirectional DC / DC converter 120 with time to reduce the DC bus Cbus voltage in response to the sudden rise in the DC bus Cbus voltage.

[0032] As can be seen, this application couples the power of the front and rear stages of the power converter by feeding forward the DC bus Cbus voltage, that is, it performs power matching between the front stage (bidirectional AC / DC converter 110) and the rear stage (bidirectional DC / DC converter 120), thereby reducing the interference of AC load fluctuations on the entire system.

[0033] As described above, since the power conversion device provided by this application can reduce or avoid fluctuations in the DC bus Cbus voltage, the bus capacitor can be made smaller compared to the prior art, which can greatly reduce the size of the power conversion device and increase its power density.

[0034] Especially when the bidirectional AC / DC converter 110 is a three-phase AC / DC converter, the existing technology requires a large bus capacitor in order to stabilize the DC bus Cbus voltage. However, the power conversion device of this application can reduce the bus capacitor size. For example, a film capacitor can be used, and its capacity can be controlled in the tens of nF level. Therefore, it is particularly suitable for three-phase AC / DC converters.

[0035] In other words, the power conversion device provided in this application can achieve both high power density and high dynamic stability.

[0036] Please refer to the following: Figure 1 And please combine Figure 3 The block diagram of the second controller according to an embodiment of this application shown includes a second controller 220 in the power conversion device. When the power converter operates in inverter mode, the second controller 220 is configured to perform: The third arithmetic unit 221 receives a bus voltage sampling signal ubus and a bus voltage reference signal Ubus_ref from the DC bus, and outputs a bus voltage difference signal ubus_d. The third compensation unit 222 receives the bus voltage difference signal ubus_d and outputs the compensated bus voltage difference signal ubus_r. The second modulation unit 223 receives the compensated bus voltage difference signal ubus_r and outputs a second switching control signal to control the switching transistors inside the bidirectional DC / DC converter 120.

[0037] That is, the bidirectional DC / DC converter 120 is controlled by the second controller 220 to stabilize the DC bus voltage at the first DC terminal of the bidirectional DC / DC converter 120.

[0038] In practical applications, the first arithmetic unit 211, the second arithmetic unit 214, and the third arithmetic unit 221 can be implemented as subtraction arithmetic units. For the first arithmetic unit 211, its positive input terminal receives the AC voltage reference signal Uacref, and its negative input terminal receives the AC voltage sampling signal uac. For the second arithmetic unit 214, its positive input terminal receives the current reference signal iLref, and its negative input terminal receives the AC current sampling signal iL. For the third arithmetic unit 221, its positive input terminal receives the bus voltage reference signal Ubus_ref, and its negative input terminal receives the bus voltage sampling signal ubus.

[0039] In practical applications, the first compensation unit 212, the second compensation unit 215 and the third compensation unit 222 can be implemented as any existing compensation unit, such as PID, PI or PD.

[0040] In practical applications, the first modulation unit 216 can be implemented as any unit that can form a first switch control signal based on the compensated AC current difference signal iL_r, and the second modulation unit 223 can be implemented as any unit that can form a second switch control signal based on the compensated bus voltage difference signal ubus_r. This application does not specifically limit either of them.

[0041] Specifically, in one embodiment, when the bus voltage sampling signal ubus is lower than the first bus voltage setting value, the limiting unit 213 sets the current reference signal to the first level and outputs the current reference signal iLref according to the compensated AC voltage difference signal Uac_r; when the bus voltage sampling signal ubus recovers to the second bus voltage setting value, the limiting unit 213 sets the current reference signal to the second level and outputs the current reference signal iLref according to the compensated AC voltage difference signal Uac_r, wherein the current reference signal at the first level is less than the current reference signal at the second level, and the second bus voltage setting value is greater than the first bus voltage setting value.

[0042] For practical applications, please refer to [the relevant documentation]. Figure 1When the power converter operates in rectification mode that converts AC power to DC power, the first controller 210 is configured to output a switching control signal for controlling the switching transistors inside the bidirectional AC / DC converter 110 based on the AC voltage sampling signal uac and AC current sampling signal iL from the AC terminal of the bidirectional AC / DC converter 110 and the bus voltage sampling signal ubus from the DC bus.

[0043] Furthermore, the second controller is configured to output a switching control signal for controlling the switching transistors within the bidirectional DC / DC converter based on the voltage sampling signal and current sampling signal from the DC output terminal (second DC terminal) of the bidirectional DC / DC converter 120, and the bus voltage sampling signal ubus from the DC bus.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A power conversion device, characterized in that, include: Power converter, including a cascaded bidirectional AC / DC converter, a DC bus and a bidirectional DC / DC converter; The first controller, when the power converter is operating in inverter mode, is configured to perform: The first processing unit receives an AC voltage sampling signal and an AC voltage reference signal from the AC terminal of the bidirectional AC / DC converter, and outputs an AC voltage difference signal. The first compensation unit receives the AC voltage difference signal and outputs the compensated AC voltage difference signal. The limiting unit receives the compensated AC voltage difference signal and the bus voltage sampling signal from the DC bus, and outputs a current reference signal. The second processing unit receives the AC current sampling signal and the current reference signal from the AC terminal, and outputs the AC current difference signal; The second compensation unit receives the AC current difference signal and outputs the compensated AC current difference signal. The first modulation unit receives the compensated AC current difference signal and outputs a first switching control signal to control the switching transistors in the bidirectional AC / DC converter.

2. The power conversion device according to claim 1, characterized in that, It also includes a second controller, which is configured to perform the following when the power converter is operating in inverter mode: The third arithmetic unit receives a bus voltage sampling signal and a bus voltage reference signal from the DC bus, and outputs a bus voltage difference signal. The third compensation unit receives the bus voltage difference signal and outputs the compensated bus voltage difference signal. The second modulation unit receives the compensated bus voltage difference signal and outputs a second switching control signal to control the switching transistors in the DC / DC converter.

3. The power conversion device according to claim 1, characterized in that, When the bus voltage sampling signal decreases, the current reference signal output by the limiting unit also decreases to ensure the stability of the DC bus voltage.

4. The power conversion device according to claim 1, characterized in that, When the bus voltage sampling signal increases, the current reference signal output by the limiting unit also increases to ensure the stability of the DC bus voltage.

5. The power conversion device according to claim 1, characterized in that, The bidirectional AC / DC converter is a PFC converter.

6. The power conversion device according to claim 1, characterized in that, The bidirectional AC / DC converter is either a single-phase converter or a three-phase converter.

7. The power conversion device according to claim 5, characterized in that, The bidirectional DC / DC converter is an LLC resonant converter.

8. The power conversion device according to claim 2, characterized in that, When the power converter operates in rectification mode that converts AC power to DC power, the first controller is configured to output a first switching control signal to control the switching transistors in the bidirectional AC / DC converter based on AC voltage sampling signals and AC current sampling signals from the AC terminal of the bidirectional AC / DC converter, and bus voltage sampling signals from the DC bus.

9. The power conversion device according to claim 8, characterized in that, The second controller is configured to output a second switching control signal to control the switching transistors within the bidirectional DC / DC converter based on voltage and current sampling signals from the DC output terminal of the bidirectional DC / DC converter and bus voltage sampling signals from the DC bus.

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