Patent Grant
7362557
1. Field of the Invention
This disclosure is generally related to power conversion, and particularly to bi-directional power conversion via a DC/DC switch mode power converter.
2. Description of the Related Art
A variety of applications employ DC/DC power conversion to, for example, step-up and/or step-down voltage. For example, electric drive or hybrid automotive applications may at times provide power from a high voltage DC source, such as one or more fuel cells, to supply low voltage DC loads and/or to recharge one or more batteries and/or ultracapacitors. During other times, a low voltage power source, such as one or more of the batteries and/or ultracapacitors, may provide power to a high voltage DC load, such as an electric traction motor coupled to drive one or more wheels via a drivetrain.
Switch mode converters typically offer higher efficiency than linear regulators, and can step-up or step-down the input voltage. In some embodiments, switch mode converters can even invert the input voltage. A variety of switch mode DC/DC converter topologies and operation of the same are known to those of skill in the art. For example, buck converters for stepping down the input voltage, boost converters for stepping up the input voltage, as well as buck-boost converters and flyback converters for alternatively stepping down and stepping up the input voltage.
DC/DC switch mode converter operation is typically limited by thermal constraints, such as the ability to dissipate heat generated by the conversion process. This may be disadvantageous, particularly where some flexibility is desired in the load pattern during boost mode operation of the DC/DC converter. It would thus be desirable to increase the flexibility of operation of the DC/DC converter, while avoiding thermal damage to the DC/DC converter from excessive accumulation of heat.
A controller implements a state machine for operating the bi-directional power converter with a flexible load pattern while maintaining a thermal condition of the power converter within acceptable limits. The state machine implements a wait loop in response to selected conditions to maintain the thermal condition.
In one embodiment, a method of operating a bi-directional power converter, the method comprises: monitoring command and condition signals; and selectively supplying control signals to cause the bi-directional power converter to cycle between a plurality of operational modes based on the monitored command and condition signals, the plurality of operational modes comprising: a ready mode; a buck mode; a boost mode; a fault mode; and a first wait mode.
In one embodiment, selectively supplying control signals comprises supplying control signals to cause the bi-directional power converter to cycle from the boost mode to the first wait mode based in part on the condition signals. In one embodiment selectively supplying control signals comprises determining whether a thermal condition has been reached based in part on the condition signals. In one embodiment, the condition signals comprise an input current.
In one embodiment, selectively supplying control signals comprises supplying control signals to cause the bi-directional power converter to cycle from the boost mode to the first wait mode when an integrated value of an input current exceeds a threshold input current by a defined value.
In one embodiment, the plurality of operational modes further comprises a second wait mode. In one embodiment, selectively supplying control signals comprises supplying control signals to cause the bi-directional power converter to operate in the first wait mode for a first defined period of time and selectively supplying control signals to cause the bi-directional power converter to operate in the second wait mode for a second defined period of time.
In one embodiment, selectively supplying control signals comprises supplying control signals to cause the bi-directional power converter to operate in the fault mode in response to detection of a fault condition. In one embodiment the method further comprises applying a hardware-based over-protection limit to the operation of the bi-directional power converter. In one embodiment the method further comprises applying a software-based over-protection limit to the operation of the bi-directional power converter.
In one embodiment, a system for controlling a power converter, comprises: a fault detection monitor configured to generate a fault signal in response to a fault condition; a state machine configured to transition between a plurality of states comprising a ready state, a boost state, a buck state, a fault state, a first wait state, and a second wait state, wherein the state machine is configured to transition from the boost state to the first wait state in response to an indication of a thermal condition; and a control signal generator configured to generate control signals for controlling the power converter based on a current state of the state machine.
In one embodiment, the state machine is configured to transition between states in the plurality of states based on a received command and the fault signal. In one embodiment, the indication of a thermal condition is a function of a current level. In one embodiment, the indication of a thermal condition is a function of a current level and time. In one embodiment the indication of a thermal condition is an integrated value of an input current in excess of a threshold input current.
In one embodiment, a system for controller a power converter comprises: means for detecting fault conditions; means for transitioning between a plurality of states comprising a boost state, a first wait state and a second wait state; and means for generating control signals coupled to the means for detecting fault conditions and the means for transitioning between a plurality of states.
In one embodiment, the means for transitioning between a plurality of states comprises a state machine implemented in a computer-readable media. In one embodiment, the plurality of states comprises a buck state and a fault state. In one embodiment, the means for transitioning is configured to transition from the boost state to the first wait state in response to an indication of a thermal condition. In one embodiment, the indication of a thermal condition is a function of an input current.
In one embodiment, a computer-readable memory medium stores instructions for causing a control system to control a power converter by: monitoring command and condition signals; and selectively supplying control signals to cause the power converter to cycle between a plurality of operational modes based on the monitored command and condition signals, the plurality of operational modes comprising: a ready mode; a buck mode; a boost mode; a fault mode; and a first wait mode. In one embodiment, the plurality of operational modes further comprise a second wait mode. In one embodiment, the stored instructions further comprise instructions for causing the control system to control the power converter by: selectively generating control signals to cause the power converter to cycle from the boost mode to the first wait mode; and selectively generating control signals to cause the power converter to cycle from the boost mode to the second wait mode.
In one embodiment, the stored instructions further comprise instructions for causing the control system to control the power converter by: selectively supplying control signals to cause the power converter to cycle from the boost mode to the first wait mode in response to an indication of a thermal condition. In one embodiment, the indication of a thermal condition is a function of an input current.
In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn, are not intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the drawings.
In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments. However, one skilled in the art will understand that other embodiments may be practiced without these details. In other instances, well-known structures associated with power converters, switched mode power converters, controllers, fuel cell systems, uninterruptible power supplies, batteries and/or ultracapacitors have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments.
Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is as “including, but not limited to.”
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Further more, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
The headings provided herein are for convenience only and do not interpret the scope or meaning of the claimed invention.
While
In particular, the high voltage power source 12 may take a variety of forms, for example, a fuel cell stack comprising a plurality of fuel cells, such as proton exchange membrane (PEM) fuel cells. The connection between the high voltage power source 12 and the power converter 16 may take place within a protective housing of the power converter 16.
The low voltage load 14 may take a variety of forms, for example, one or more low voltage devices such as monitoring or control systems for the power system 10 or a device associated with the power system 10, for example an electric or hybrid vehicle. The low voltage load 14 may additionally, or alternatively comprise one or more power storage devices, such as one or more batteries and/or one or more ultracapacitors, which act as low voltage loads while being recharged, and act as low voltage power sources when being discharged.
The high voltage load 24 may take a variety of forms such as a high voltage traction drive motor, and/or one or more high voltage auxiliary drive motors such as a compressor, fan and/or pump associated with the power system 10 and/or a device associated with the power system 10 such as an electric or hybrid vehicle.
The power converter 16 may provide galvanic isolation between the high and low voltage buses 18, 20, respectively, for example via a transformer (not shown). The power converter 16 is operable to adjust voltage output in response to pulse width modulated (PWM) input signals. Thermal cooling may be provided by a glycol electronics cooling loop, for example, with a flow rate of approximately 8 liters/minute. The power converter 16 may also include suitable automatic over load and/or over temperature features for reducing or shedding load and/or heat.
The controller 22 may take a variety of forms such as a programmed or programmable microprocessor, digital signal processor (DSP), application specific integrated circuit (ASIC), and/or discrete circuit. The controller 22 provides control signals to one or more switches in the power converter 16. The controller 22 may receive input signals from one or more sensors and/or devices. For example, the controller 22 may receive high voltage side voltage and/or current measurements from voltage sensor 26a and/or current sensor 26b. Additionally, or alternatively, the controller 22 may receive low voltage side voltage and/or current measurements from voltage sensor 28a and/or current sensor 28b. Additionally or alternatively, the controller 22 may receive signals from actuators or sensors associated with other components of the power system 10, such as pedals, motors, compressors, fans, etcetera.
With continuing reference to
The power system 10 may provide the signals to the controller 22 via a signal interface as set out in Table A, below.
Suitable input characteristics for an example power converter 16 operating in boost mode are set out in Table B, below.
Suitable output characteristics for an example power converter 16 operating in boost mode are set out in Table C, below.
Suitable input characteristics for an example power converter 16 operating in buck mode are set out in Table D, below.
Suitable output characteristics for an example power converter 16 operating in buck mode are set out in Table E, below.
The state machine 40 comprises a number of distinct states including: a ready state 42a, buck state 42b, boost state 42c, faulted state 42d, short wait state (e.g., wait 5 seconds) 42e, long wait state (e.g., wait 60 seconds) 42f, the order of the states being denominated in the circles representing the states as 0-5, respectively. The state machine 40 comprises a number of transitions defined between the states, the transitions illustrated by arrows 44a-44u, the order of the transitions being denominated between the head and tail of the arrows as 1-21, respectively. The transition order implies precedence. Thus, for example, if the state is Boost 42c, the condition for the transition 44m to the state Wait 60 seconds 42f is checked first, and if the condition is TRUE the state transition is made without checking any other conditions.
Outputs are persistent, thus if no action is taken to change any of the outputs during a given execution of the state machine 40, the last values for all of the outputs will be used. If none of the conditions for state transition are met, the state does not change, and no actions are taken. Only one state transition occurs per execution of the state machine 40. An appropriate fault bit is set if, and when, a fault occurs. A hardware, software or EPO fault detected by the power converter 16 or an integrated power train is identified as a DC_DC_FAULT.
Table F shows a number of suitable values for a pair of operating parameters for an example power converter 16, that may be calibrated.
The operation of the state machine 40 is set out in Table G, immediately below.
When operating In boost mode, some exemplary efficiencies for the power converter 16 are: 1) greater than 80% from 30% Pmax to Pmax (8.5V<ULV<11V); and 2) greater than 85% from 30% Pmax to Pmax (ULV equal to or greater than 11V). When operating in buck mode some exemplary efficiencies for the power converter 16 are: 1) greater than 85% from 30% Pmax to Pmax (UHV equal to or greater than 350V); and 2) greater than 88% from 30% Pmax to Pmax (250V<UHV<350V).
In some embodiments, the output voltage may vary by approximately 2% from the rated voltage in both boost and buck modes. An AC overlay in the load circuit may be lower than 3% TRMS against the average value.
Table H shows a number of example fault conditions, with corresponding variable names, data types, error types, reset values, and comments.
In an ideal case, the boost mode would be able to run forever, at least until the low voltage power source (e.g., 12V battery and/or ultracapacitors) are discharged. Of course, some power converter 16 designs will overheat if forced to operate essentially continuously, due, for example, to thermal limitations which may exist where the thermal design was primarily based on the load pattern illustrated in
The load pattern may be changed in a flexible manner, instead of a fixed load pattern 50, while maintaining a thermal condition equivalent to that of the load pattern of
It is however, difficult to predict the boost mode ON time precisely, particularly since it is related to many factors, such as coolant temperature, coolant flow rate, operating history, power level and duration. Using I2t-criteria as an indication of the thermal condition may be useful.
In one embodiment, 350 A with 5 second duration would have an I2t value of 612,500 A2S. If the input current reduced in half, the boost mode ON time can be extended as long as 20 seconds to allow the same amount of I2t pass through. Using the same method, results in a boost mode ON time estimation curve 52 are illustrated in
The proposed load pattern change would, instead of setting a 5 second fixed boost mode ON time, would allow the integrated powertrain (IPT) software to calculate the ON time based on the low voltage input I2t. Once the low voltage input I2t reaches the 612,500 A2S, the IPT software disables boost mode, sending a message back to a vehicle controller indicating that the power converter boost mode goes into a 5 second break period. After the 5 second break, the vehicle controller may enable the power converter boost mode again. If the vehicle controller enables the power converter boost mode during the 5 second break period, the IPT controller will hold the command until the 5 second break period ends.
In reality the low voltage input current LV_I is not constant, thus the controller may employ an integral operation (e.g., ∫I2dt) to accumulate the total I2t. Since the boost mode can run continuously at 150 A or less, the integral only counts when the low voltage input current LV_I is greater than 150 A.
In boost mode in some embodiments, if the battery voltage is over, for example, 13V for a short period of time, there will be no problem. Where the low voltage power source is a battery, the battery terminal voltage will drop under 13V once the battery is loaded.
In one embodiment, the start-up load condition in boost mode is 1.7 kOhm/13 mF, in which 1.7 kOhm is the total bleeding resistance, and the 13 mF is the total HV bus capacitance. It is possible to loosen the capacitance limitation if this requirement does not completely reflect a real situation, such as that for a vehicle. It is also possible to implement a high voltage capacitance in power system 10, for example a high voltage capacitance of between 8.4 mF and 13 mF. In such a case, an additional bleeding resistance, other than 2.5K inside the integrated power train, should be added to make sure boost operation starts up properly, because the DC/DC in boost mode takes advantage of the 1.7 kOhm bleeding resistor for a minimum load. If the command voltage in boost mode is higher than 250V, the resistance could be higher than 1.7 kOhm to keep the same minimum load. Table I, below, shows the total resistance and the additional resistance at different voltages. If the commanded high voltage is higher than 310V, no extra resistance is needed.
The power system 10 may employ a number of hardware and/or software implemented protections. For example, a first hardware implemented overvoltage protection scheme may limit high voltage in buck mode to 445V while a second hardware implemented overvoltage protection scheme limits high voltage in boost mode to 426.8V. Additionally, or alternatively, a software implemented overvoltage protection scheme may limit high voltage to 440V.
The controller 102 may be implemented in a variety of ways, including as separate subsystems. The controller 102 may be implemented as a microprocessor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a gate-driver board, or the like, or as a series of instructions stored in a memory, such as the memory 106 and executed by a processor, such as the processor 104, or various combinations of the above. Thus, software modifications to existing hardware may allow the implementation of the controller 102. Various modules, such as the state machine 110, are identified as separate blocks in the functional block diagram of
While the illustrated embodiment denotes a single processor 104, other embodiments may comprise multiple processors. The memory 106 may comprise, for example, registers, read only memory (“ROM”), random access memory (“RAM”), flash memory and/or electronically erasable programmable read only memory (“EEPROM”), and may provide instructions and data for use by the controller 102.
The fault detection module 108 determines whether conditions exist indicating a system fault and generates fault signals in response thereto. For example, the fault detection module may monitor system conditions as indicated by sensors 26a, 26b, 28a, 28b and control signals to determine whether a fault condition exists such as the fault conditions set forth in Table H. In response to detection of a fault condition, the fault detection module may generate fault signals.
The state machine 110 comprises a number of distinct states, such as those described above with respect to
Those skilled in the relevant art can readily create source code based on the Tables, Figures and the detailed description provided herein.
The term “computer-readable medium” as used herein refers to any medium that participates in providing instructions to a system or a processor for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media includes, for example, hard, optical or magnetic disks. Volatile media includes dynamic memory. Transmission media includes coaxial cables, copper wire and fiber optics. Transmission media can also take the form of acoustic or light waves, such as those generated during radio wave and infrared data communications.
Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, or any other magnetic medium, a CD-ROM, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, EPROM and an EEPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave, or any other medium from which a computer can read.
Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to a processor for execution. For example, the instructions may initially be carried on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system can receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal. An infrared detector coupled to a system bus can receive the data carried in the infrared signal and place the data on system bus. The system bus carries the data to system memory, from which a processor retrieves and executes the instructions. The instructions received by system memory may optionally be stored on storage device either before or after execution by the processor.
Although specific embodiments of, and examples for, the apparatus and method of bi-directional power conversion are described herein for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the disclosure, as will be recognized by those skilled in the relevant art. The teachings provided herein can be applied to other power systems, not necessarily the exemplary electric or hybrid vehicle based system generally described above. Likewise, the teachings provided herein can be applied to other power sources, not necessarily the exemplary fuel cell system, battery and/or ultracapacitors based power sources generally described above.
The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, including but not limited to patents U.S. Pat. No. 5,402,059, issued Mar. 28, 1995; U.S. Pat. No. 6,646,837, issued Nov. 11, 2003; U.S. Pat. No. 6,452,815, issued Sep. 17, 2002; and U.S. Pat. No. 6,587,356, issued Jul. 1, 2003; U.S. application Ser. No. 10/658,559, filed Sep. 8, 2003; Ser. No. 09/683,317, filed Dec. 13, 2001; Ser. No. 10/118,659, filed Apr. 8, 2002; Ser. No. 09/848,482, filed May 3, 2001; Ser. No. 10/345,894, filed Jan. 15, 2003; Ser. No. 10/346,561, filed Jan. 16, 2003; Ser. No. 10/360,832, filed Feb. 7, 2003; and Ser. No. 10/298,473, filed Nov. 18, 2002; and U.S. Provisional Application Ser. No. 60/246,273, filed Nov. 6, 2000; Ser. No. 60/255,371, filed Dec. 13, 2000; Ser. No. 60/270,703, filed Feb. 22, 2001; Ser. No. 60/271,184, filed Feb. 23, 2001; Ser. No. 60/319,070, filed Jan. 16, 2002; Ser, No. 60/319,071, filed Jan. 16, 2002; and Sere. No. 60/319,116, filed Feb. 20, 2002; are incorporated herein by reference, in their entirety. Aspects of the disclosure can be modified, if necessary, to employ systems, circuits and concepts of the various patents, applications and publications to provide yet further embodiments.
These and other changes can be made to the disclosed embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the disclosure to the specific embodiments disclosed in the specification and the claims, but should be construed to include bi-directional power converter based systems and methods operate in accordance with the claims. Accordingly, the disclosure is not limited by the embodiments, but instead its scope is to be determined entirely by the following claims.
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