Electrical energy storage interfaces and methods for storage inverters

Abstract

An initial operating condition for a bidirectional power converter is determined, and transitions between the initial operating condition and a steady state operating condition for the bidirectional power converter are controlled. The bidirectional power converter includes first terminals to be coupled to an electrical energy storage device and second terminals to be coupled to an inverter, and is operable to scale voltage between a first voltage at the first terminals for the electrical energy storage device and a second voltage at the second terminals for the inverter. The initial operating condition is determined based on a first sensed voltage of the electrical energy storage device and a second sensed voltage of the inverter. The transitions include a transition from the initial operating condition to the steady state operating condition, and a transition to return to the initial operating condition from the steady state operating condition.

Description

92557188ELECTRICAL ENERGY STORAGE INTERFACES AND METHODS FOR STORAGE INVERTERSFIELD

[0001] The present application relates generally to power electronics and storage inverters, and in particular to electrical energy storage interfaces and methods.BACKGROUND

[0002] Interfaces to electrical energy storage devices in storage inverters traditionally provide voltage and current sensing for managing the available storage capacity and limiting the voltage and current when charging and discharging such that the electrical energy storage device is not damaged. In some cases, the electrical energy storage interface provides scaling of the voltage and current to levels that are appropriate for the inverter stage to operate correctly. In many systems, it is common to allow some alternating current (AC) to flow through the electrical energy storage device. This AC current may be a combination of the inverter output frequency and associated harmonic frequency components, and components at the switching frequency and those associated harmonic frequencies of the inverter and other power conversion circuits. In many systems, AC current flowing within the electrical energy storage device has the effect of reducing the device life because of the increased dissipated heat and resulting increased temperature, and because AC current can impose small, highly repetitive charge-discharge cycles . In addition, the higher frequency current and voltage components flowing to the electrical energy storage device, and its cables, can increase radiated electromagnetic interference emitted from a system.

[0003] Improved storage interfaces and methods are desirable.SUMMARY

[0004] The present disclosure encompasses embodiments, such as electrical energy storage interface circuits and methods, that that may help, for example, reduce aging, wear out and stress on an electrical energy storage device to which a storage inverter is coupled.92557188

[0005] Embodiments described herein may provide the functions of scaling the electrical energy storage device voltage to / from an appropriate voltage for the inverter and sensing the electrical energy storage device voltage and current. In addition, scaling of initial conditions and controlled transition to steady state conditions may be provided to control currents and limit stress when an electrical energy storage device is first connected and / or when the inverter begins operation. Active methods are also provided to substantially eliminate or at least reduce AC currents flowing through and AC voltage applied to the electrical energy storage device.

[0006] Examples of features or functions that may be provided in embodiments, alone or in any of various combinations, include the following: scaling of voltage between the electrical energy storage device and a direct current (DC) terminal voltage of the inverter; electrical energy storage device voltage and current sensing for limiting the voltage and current when charging and discharging; scaling for initial conditions and ramping to operating conditions such that currents are controlled upon startup; bi-directional power conversion to / from the electrical energy storage device and the DC terminal voltage of the inverter; fault disconnect of the electrical energy storage device in the event of an overcurrent, over-voltage, under-voltage, temperature extreme, other condition(s) that may be harmful to the device; blocking inverter AC voltage (50 / 60 Hz, for example) and harmonic ripple current from flowing through the electrical energy storage device, for example by directing the ripple current through grid ripple capacitance; cancelling switching rate (and harmonic) ripple current from a power conversion circuit such that it does not flow through the electrical energy storage device.92557188

[0007] According to one aspect of the present disclosure, an electrical energy storage interface includes a bidirectional power converter and a startup controller, coupled to the bidirectional power converter. The bidirectional power converter includes first terminals to be coupled to an electrical energy storage device and second terminals to be coupled to an inverter, and is operable to scale voltage between a first voltage at the first terminals for the electrical energy storage device and a second voltage at the second terminals for the inverter. The startup controller is operable to determine an initial operating condition for the bidirectional power converter based on a first sensed voltage of the electrical energy storage device and a second sensed voltage of the inverter, and to control transitions between the initial operating condition and a steady state operating condition for the bidirectional power converter. The transitions include a transition from the initial operating condition to the steady state operating condition, and a transition to return to the initial operating condition from the steady state operating condition.

[0008] According to another aspect of the present disclosure, a method involves determining an initial operating condition for a bidirectional power converter, and controlling transitions between the initial operating condition and a steady state operating condition for the bidirectional power converter. The bidirectional power converter includes first terminals to be coupled to an electrical energy storage device and second terminals to be coupled to an inverter, and is operable to scale voltage between a first voltage at the first terminals for the electrical energy storage device and a second voltage at the second terminals for the inverter. The determining involves determining the initial operating condition for the bidirectional power converter based on a first sensed voltage of the electrical energy storage device and a second sensed voltage of the inverter. The transitions include a transition from the initial operating condition to the steady state operating condition, and a transition to return to the initial operating condition from the steady state operating condition.

[0009] Other aspects and features of embodiments of the present disclosure will become apparent to those ordinarily skilled in the art upon review of the following description.92557188BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Embodiments will be described herein, by way of example only, with reference to the accompanying drawings.

[0011] Fig. 1 illustrates an example of an electrical energy storage interface according to an embodiment.

[0012] Fig. 2 illustrates an example of a bidirectional power converter.

[0013] Fig. 3 illustrates an example of a bidirectional converter element.

[0014] Fig. 4 illustrates an example of a grid frequency ripple rejector.

[0015] Fig. 5 illustrates an example of a startup controller.

[0016] Fig. 6 illustrates an example of a fault protector.

[0017] Fig. 7 illustrates an example of a ripple current canceller.

[0018] Fig. 8 illustrates an example method according to an embodiment.DETAILED DESCRIPTION

[0019] Fig. 1 illustrates an example electrical energy storage interface 100 according to an embodiment. Electrical energy storage interface 100 is connected to a battery as the electrical energy storage device 108 in Fig. 1, but it should be appreciated that this is one illustrative example of an interface and electrical energy storage device. Although batteries are commonly used to store electrical energy in operation with storage inverters, the present disclosure is not in any way limited to batteries or any other type of electrical energy storage elements or devices. Electrical energy storage interface 100 includes bidirectional power converter 104, grid frequency ripple rejector 112, startup controller 120, fault protector 124, AC terminals 128, inverter 132, grid ripple capacitance 134, and ripple current canceller 136.

[0020] The example electrical energy storage interface 100 is an interface to an electrical energy storage device for a storage inverter, and for completeness the electrical energy storage device 108 and an inverter 132 are also shown in Fig. 1. It should be appreciated, however, that92557188 embodiments herein focus primarily on interfaces and related methods rather than electrical energy storage devices or inverters.

[0021] A battery is shown in Fig. 1 at 108 as an example of an electrical energy storage device, and may be of any type. Embodiments herein are not in any way restricted to any particular type of battery, or to an electrical energy storage device that includes a battery. For example, the battery at 108 may include several cells or batteries connected in series and / or several cells or batteries connected in parallel. Electrical energy storage devices may include one or more electrical energy storage elements, such as one or more batteries, other electrochemical storage elements, storage capacitors, inductors or inductive elements, and / or other types of electrical energy storage elements. More than one type of electrical energy storage element may be provided in some embodiments.

[0022] Although embodiments are not necessarily limited to any particular type of electrical energy storage device, an interface may include or support features that are adapted or beneficial for certain electrical energy storage devices. For example, voltage of a battery does not tend to change significantly with its level of charge, but this property of batteries does not extend to all other types of electrical energy storage devices. Therefore, in some implementations an interface may be designed to accommodate this property, whereas in other implementations an interface may be designed to accommodate or exploit more significant changes in voltage depending on the level of charge of the electrical energy storage device.

[0023] Inverter 132 is preferably a bidirectional DC to AC inverter, which may also be referred to as a DC / AC inverter or DC / AC converter. Various possible implementations of such inverters will be known to those familiar with DC / AC power conversion. Embodiments disclosed herein are not in any way restricted to particular types of inverters.

[0024] Grid ripple capacitance 134 may include a single capacitor, or several capacitors coupled together in series and / or in parallel.

[0025] Illustrative example implementations of other components in Fig. 1, and operation thereof, are provided below.92557188

[0026] Fig. 2 illustrates an example of bidirectional power converter 104 in Fig. 1. In Fig. 2, the example bidirectional power converter 200 includes first DC power terminals 204 which may also be referred to as electrical energy storage device terminals, bidirectional converter elements 208-1 and 208-n, converter controller 224, and second DC power terminals 228. Converter controller 224 receives input signals including a phase shift control signal as shown at 212, a shutdown signal as shown at 216, and a compensated error signal as shown at 220 in the example shown.

[0027] Bidirectional converter elements 208-1 and 208-n are intended to represent two elements of a plurality (two or more) of bidirectional converter elements, with first terminals of each element coupled in parallel to first DC power terminals 204, and second terminals of each element coupled in parallel to second DC power terminals 228. In general, there may be an integer number “n” of such elements, in which case bidirectional converter element 208-1 may be referred as a first bidirectional converter element and bidirectional converter element 208-n may be referred to as an nthbidirectional converter element. The illustrated connections to first DC power terminals 204 and second DC power terminals 228, between bidirectional converter elements 208-1 and 208-n are intended to illustrate how terminals of each bidirectional converter element are coupled to the DC power terminals in embodiments that include more than two bidirectional converter elements.

[0028] Fig. 3 illustrates an example of a bidirectional converter element, which may be implemented at 208-1 and 208-n in Fig. 2. In this example, the bidirectional converter element 300 includes first DC power terminals 304 to be coupled to first DC power terminals 204 in Fig. 2, first capacitance 308 coupled across the first DC power terminals 304, switches 312 coupled in parallel with (across) first DC power terminals 304, inductance 316 coupled to a point between the switches 312 and one of second DC power terminals 320 that are to be coupled to second DC power terminals 228 in Fig. 2, and second capacitance 324 coupled across second DC power terminals 320.

[0029] Switches 312 may, by way of example, be metal oxide semiconductor field-effect transistors (MOSFETs). Each of the switches 312 may be comprised of a single switch or several switches coupled in series and / or in parallel. Each of first capacitance 308 and second92557188 capacitance 324 may include a single capacitor, or several capacitors coupled together in series and / or in parallel. Inductance 316 may include a single inductor, or several inductors coupled together in series and / or in parallel.

[0030] Fig. 3 is an illustration of a buck converter topology in which control is achieved by pulse width modulation. Any of various other converter topologies are possible as implementation examples of a bidirectional converter element. In such other converter topologies, control may be achieved, for example, by pulse width modulation, frequency modulation, or phase shift modulation.

[0031] Fig. 4 illustrates an example of the grid frequency ripple rejector 112 in Fig. 1. The example grid frequency ripple rejector 400 includes storage voltage sense terminals 408, storage voltage sense element 412, grid ripple capacitance voltage sense terminals 416, grid ripple capacitance voltage sense element 420, AC voltage and harmonic rejector 428 coupled to grid ripple capacitance voltage sense element 420, difference block 432 coupled to AC voltage and harmonic rejector 428, compensated error generator 436 coupled to difference block 432, and multiplier 444 coupled to the storage voltage sense element 412 and to difference block 432. In the example grid frequency ripple rejector 400, a ramp control signal is received as an input signal as shown at 404, and a compensated error signal is generated as an output signal as shown at 440.

[0032] 50 or 60 Hz are examples of the frequencies present at a typical inverter output; other frequencies are possible.

[0033] Difference block 432 has a polarity that is determined by the topology of bidirectional converter elements (such as the example 300 in Fig. 3) of the bidirectional power converter (104 in Fig. 1). The polarity of difference block 432 in Fig. 4 is illustrated as an example, for bidirectional converter element 300 in Fig. 3, but may be the same or inverted for other possible bidirectional converter element topologies, in order to provide negative feedback in a servo loop formed by grid frequency ripple rejector 112 shown in Fig. 1.

[0034] Voltage sense elements 412 and 420 may be or include a voltage sensor or device such as a voltmeter or other voltage sensor. Other types of voltage sensors or devices will be92557188 apparent to those familiar with power electronics and control. Embodiments are not restricted to any particular type of voltage sense element. AC voltage and harmonic rejector 428 may include, for example, a low pass filter or a comb rejection filter to provide signal processing action to remove or at least reduce the frequencies and associated harmonics from the signal from grid ripple capacitance voltage sense element 420. Compensated error generator 436 may include, for example, a gain block, a low pass filter block, or a combination of these blocks.Embodiments are not restricted to these two types of blocks. Various implementation options for multiplier 444 and difference block 432 will be readily apparent to those familiar with power conversion, power electronics, and power electronics control.

[0035] Fig. 5 is an example of startup controller 120 in Fig. 1. In Fig. 5, the example startup controller 500 includes storage voltage sense terminals 512, storage voltage sense element 516, grid ripple capacitance voltage sense terminals 520, grid ripple capacitance voltage sense element 524, initial conditions controller 532, and ramp rate and trajectory controller 536. A shutdown signal is shown at 504, a storage side capacitance charging complete signal is shown at 508, and a grid ripple capacitance charging complete signal is shown at 528. These signals are received as input signals. A ramp control signal, shown at 540, is generated as an output signal.

[0036] Storage voltage sense element 516 and grid ripple capacitance voltage sense element 524 may be the same as, or implemented separately from, storage voltage sense element 412 and grid ripple capacitance voltage sense element 420 of Fig. 4, respectively.Implementation of storage voltage sense element 412 and grid ripple capacitance voltage sense element 420 and / or storage voltage sense element 516 and grid ripple capacitance voltage sense element 524 in Fig. 5 may, by way of example, be analog to digital converters. Initial conditions controller 532 and ramp rate and trajectory controller 536 may, by way of example, be implemented as digital logic functions. These functions may be implemented using digital logic gates or in firmware controlling a microcontroller, for example.

[0037] Fig. 6 is an example of fault protector 124 in Fig. 1. The example fault protector 600 in Fig. 6 receives input signals including a shutdown reset signal as shown at 604, an inverter shutdown request signal as shown at 608, a discharging over-current signal as shown at 612, a charging over-current signal as shown at 616, an over-temperature signal as shown at 620,92557188 an under-voltage signal as shown at 624, and an over-voltage signal as shown at 628, and generates a shutdown signal, as shown at 640, as an output signal. The input signals are received by respective shutdown latches and reset blocks 632, which are in turn coupled to inputs of OR gate 636. The aforementioned input signals are examples of shutdown signals that may occur in an inverter. Other input signals that initiate a shutdown event may be implemented in other inverter examples.

[0038] Various implementation examples of latches and reset blocks such as those shown at 632 and OR gates such as the OR gate shown at 636 will be apparent to those familiar with power conversion, power electronics, and power electronics control.

[0039] Fig. 7 is an example of ripple current canceller 136 of Fig. 1. The example ripple current canceller 700 receives a power level signal as an input signal as shown at 704, includes power level parser 708 coupled to phase offset generator 712, and generates a phase shift control signal as an output signal as shown at 716.

[0040] Power level parser 708 and phase offset generator 712 may, by way of example, be implemented as digital logic functions. These functions may be implemented using digital logic gates or in firmware controlling a microcontroller, for example.

[0041] Turning now from example interface structure and implementations to operation, with reference first to Figs. 1 and 4 the voltage at electrical energy storage device 108 is provided to grid frequency ripple rejector 112. This voltage is received at terminals 408 in Fig. 4, and sensed by storage voltage sense element 412.

[0042] For completeness, it is noted a terminal pair is shown at 408 in Fig. 4, but a single connection between electrical energy storage device 108 and grid frequency ripple rejector 112 is shown in Fig. 1. A second terminal connection is not shown in Fig. 1 in order to avoid further congestion in the drawing. It should also be noted that there may be only one connection, where there is a common ground or reference. Other terminal pairs may similarly have a second connection that is not shown in Fig. 1, or a second local connection to a common ground or reference.92557188

[0043] Storage voltage sense element 412 converts the storage voltage at terminals 408 from an analog voltage to a first digital signal. This first digital signal is provided to multiplier 444. It should be appreciated that the storage voltage sense element 412 may provide an analog signal to the multiplier 444. In this example, multiplier 444 may be an analog multiplier.

[0044] More generally, elements or functions illustrated in Fig. 4 and / or in other drawings, or otherwise disclosed herein, may be implemented digitally or as analog elements or functions. Therefore, elements or functions may receive digital or analog input signals, and generate digital or analog output signals.

[0045] The voltage from grid ripple capacitance 134 is provided to grid frequency ripple rejector 112 at terminals 416 in Fig. 4. This voltage is sensed by grid ripple capacitance voltage sense element 420, where it is converted from an analog voltage to a second digital signal. This second digital signal is provided to inverter AC voltage and harmonic rejector 428. Inverter AC voltage and harmonic rejector 428 receives this second digital signal and processes it to remove inverter AC frequencies and associated harmonics. The processing action to remove the inverter AC frequencies and associated harmonics may be provided, by way of example, by a low pass filter or a comb rejection filter. The resultant signal that is substantially free of inverter AC frequencies and associated harmonics is provided to a first input of difference block 432. It should be appreciated that grid ripple capacitance voltage sense element 420 may provide an analog signal to inverter AC voltage and harmonic rejector 428. In this example, inverter AC voltage and harmonic rejector 428 may be implemented as an analog filter.

[0046] Herein, “substantially free” refers to inverter AC frequency and associated harmonics components being reduced in an output signal of inverter AC voltage and harmonic rejector 428 relative to its input (the second digital signal from grid ripple capacitance voltage sense element 420). The reduction in inverter AC frequency signals and associated harmonics may reduce the level of those signals and harmonics in an output signal to less than one tenth of the level of those signals and harmonics in an input signal, for example, and here “less than one tenth” is an example of “substantially free”.

[0047] Multiplier 444 receives the first digital signal, which is a representation of the electrical energy storage voltage from storage voltage sense element 412.92557188

[0048] Startup controller 120 of Fig. 1 provides a ramp control signal to grid frequency ripple rejector 112. Grid frequency ripple rejector 112 receives the ramp control signal at 404 and provides it to multiplier 444.

[0049] Multiplier 444 utilizes the first digital signal and the ramp control signal to produce a product signal which is created by the multiplication of this first digital signal and the ramp control signal. The resultant product signal is provided to a second input of difference block 432.

[0050] Difference block 432 receives, at its first input, the signal from inverter AC voltage and harmonic rejector 428 that is substantially free of inverter AC frequencies and associated harmonics, and, at its second input, the product signal from multiplier 444. Difference block 432 provides a difference signal, that is the difference between these two signals, as an output signal that is sent from difference block 432 to compensated error generator 436.

[0051] Compensated error generator 436 receives the difference signal from difference block 432 and generates a compensated error signal as shown at 440, by applying gain and / or low pass filtering for example. The compensated error signal is sent to the control input of bidirectional power converter block 104 of Fig. 1, and is received at 220 in Fig. 2.

[0052] A shutdown signal is received by startup controller 120 from fault protector 124. This shutdown signal is shown at 504 in Fig. 5, and is provided to initial conditions controller 532 and to ramp rate and trajectory controller 536 in Fig. 5. Storage side capacitance charging complete signal at 508 and grid ripple capacitance charging complete signal at 528 may be received from the control system of inverter 132, for example, and are also provided to initial conditions controller 532.

[0053] The storage side capacitance charging complete signal at 508 in this example is a signal that indicates when the storage side capacitance that appears across first DC power terminals 204 of bidirectional power converter 200 in Fig. 2is fully charged. The storage side capacitance is initially charged when electrical energy storage device 108 in Fig. 1 is first connected to electrical energy storage interface 100. The storage side capacitance (not shown) is92557188 an internal capacitance of electrical energy storage interface 100 of Fig. 1 and appears across first DC power terminals 204 in Fig. 2 and across electrical energy storage device 108 in Fig. 1.

[0054] The grid ripple capacitance charging complete signal at 528 in this example is a signal that indicates when grid ripple capacitance 134 of Fig. 1 is fully charged.

[0055] For startup control, the voltage at electrical energy storage device 108 is provided to startup controller 120. This voltage is received at storage voltage sense terminals 512 in Fig. 5, and is sensed by storage voltage sense element 516. Storage voltage sense element 516 converts the voltage at storage voltage sense terminals 512 from an analog voltage to a first digital signal in some embodiments. This first digital signal is provided to initial conditions controller 532.

[0056] The voltage from grid ripple capacitance 134 is provided to startup controller 120 at grid ripple capacitance voltage sense terminals 520 in Fig. 5. This voltage is sensed by grid ripple capacitance voltage sense element 524, where it is converted from an analog voltage to a second digital signal in some embodiments. This second digital signal is provided to initial conditions controller 532.

[0057] Initial conditions controller 532 waits to receive the grid ripple capacitance charging complete signal at 528 and the storage side capacitance charging complete signal at 508. If the shutdown signal at 504 is false, then initial conditions controller 532 processes the first digital signal from storage voltage sense element 516 and the second digital signal from grid ripple capacitance voltage sense element 524 to produce a starting value of a ramp. This starting value of the ramp is provided to ramp rate and trajectory controller 536 by initial conditions controller 532. If the shutdown signal at 504 becomes true, then initial conditions controller 532 returns to the state of waiting to receive the grid ripple capacitance charging complete signal at 528 and the storage side capacitance charging complete signal at 508.

[0058] Ramp rate and trajectory controller 536 receives the starting value of the ramp from initial conditions controller 532 and begins to ramp the ramp control signal at 540 from said starting value by incrementing the ramp control signal at 540. Ramp rate and trajectory controller 536 continues to ramp the ramp control signal at 540 until it reaches the predetermined ramp final value which may be provided by a control system of inverter 132, for example. This control92557188 system may also be referred to herein as an inverter control system. Ramp rate and trajectory controller 536 then continuously produces this ramp final value as the ramp control signal at 540. If the shutdown signal at 504 becomes true, then ramp rate and trajectory controller 536 decrements the ramp control signal at 540 to a ramp reinitialization value which may be provided by a control system of inverter 132, for example. Said ramp reinitialization value returns the potential at second DC power terminals 228 in Fig. 2 and across grid ripple frequency capacitor 134 in Fig. 1 to a known voltage and remains at said voltage until initial conditions controller 532 again provides a starting ramp value. The ramp control signal 540 is provided to grid frequency ripple rejector 112 of Fig. 1. An example of grid frequency ripple rejector 112 is shown at 400 of Fig. 4.

[0059] The shutdown signal at 504 in Fig. 5 is received from fault protector 124 in Fig. 1. Fig. 6 shows an example fault protector 600. The input signals at 608, 612, 616, 620, 624, 628 are signals received from the inverter control system in some embodiments, and are examples of signals that can cause a shutdown of the electrical energy storage interface 100 of Fig. 1. It should be appreciated that these shutdown signals are examples of what may be referred to as shutdown sources, and fewer, more, and / or different shutdown sources are possible. The shutdown reset signal at 604, also provided by the inverter control system, may be a digital word that includes multiple bits, for example, and controls the reset of shutdown latches and reset blocks 632. This enables inverter 132 to control reset of fault shutdown events. OR gate 636 generates the shutdown signal at 640 when any of the input signals at 608, 612, 616, 620, 624, 628 (or shutdown sources) indicate a shutdown event. The shutdown signal at 640 is presented to startup controller 120 (and bidirectional power converter 104) of Fig. 1 from fault protector 124 of Fig. 1.

[0060] Bidirectional converter block 200 of Fig. 2 is an example of bidirectional converter 104 of Fig. 1. Converter controller 224 receives the shutdown signal as shown at 216 from fault protector 124 of Fig. 1, the phase shift control signal as shown at 212 from ripple current canceller 136 of Fig. 1, and the compensated error signal as shown at 220 from grid frequency ripple rejector 112 of Fig. 1. Converter controller 224 uses these signals to produce a control signal that is provided to bidirectional converter elements 208-1 and 208-n. By way of92557188 example, this control signal may be a pulse width modulation signal, a frequency modulation signal, or a phase shift modulation signal. This control signal provides control of the energy flow of bidirectional converter elements 208-1 and 208-n, provides control of the phase of the switching of bidirectional converter elements 208-1 and 208-n, and provides a means to individually enable or disable bidirectional converter elements 208-1 and 208-n.

[0061] An example of bidirectional converter element 208-1 in Fig. 2 is shown as bidirectional converter element 300 in Fig. 3. First capacitance 308 provides a path for switching currents from switches 312, and is coupled in parallel with (in a circuit path across or between) first DC power terminals 304. Switches 312 are coupled in parallel with (in a circuit path across) first capacitance 308, and switch the DC voltage at first DC terminals 304 and across first capacitance 308 to provide a pulse width modulated switching waveform with an amplitude equal to the potential across or between first DC power terminals 304. Inductance 316 and second capacitance 324 are coupled in a circuit path across or between switched terminals of one of the switches 312, and integrate said pulse width modulated switching waveform to produce a DC voltage at second DC power terminals 320. Switches 312 receive drive control signals from converter controller 224 of Fig. 2. In this example, the drive control signals include a pulse width modulation control drive signal.

[0062] The phase shift control signal as shown at 212 of Fig. 2 is provided by ripple current canceller 136 of Fig. 1.

[0063] In Fig. 7, ripple current canceller 700 is an example of ripple current canceller 136 of Fig. 1. The power level signal at 704 is a control signal, which may be received from the inverter control system, for example, and is presented to power level parser 708. Power level parser 708 parses the power level signal at 704 to determine the number, m, of the total number n of bidirectional converter elements 208-1 and 208-n in Fig. 2 to activate, where m is less than or equal to n. Phase offset generator 712 receives the number of active elements, m, from power level parser 708, and determines the phase shift between active bidirectional converter elements. The phase shift is equal to 360° / m. The phase for each element is determined starting from the first element and shifting the phase of each element by the phase shift. The phase shift control signal at 716 indicates this information of the phase shift and the enable state of the elements.92557188The phase shift control signal at 716 is presented to bidirectional power converter block 104 of Fig. 1. The first bidirectional converter element 208-1 up to the mthbidirectional active element are enabled. All remaining bidirectional converter elements from the (m+l)thbidirectional converter element to the nthbidirectional converter element 208-n in Fig. 2 are inhibited (not enabled).

[0064] In Fig. 1, electrical energy storage interface 100 uses bidirectional power converter 104 to convert power from electrical energy storage device 108 to inverter 132. This is also referred to herein as “scaling”. Bidirectional power converter 104 provides a mechanism to match energy storage at one potential to the DC terminals of an inverter for which a different potential is preferred or required for optimal operation. In this way, bidirectional power converter 104 steps the voltage at electrical energy storage device 108 up / down to supply the appropriate voltage at the DC terminals of inverter 132 when supplying energy from electrical energy storage device 108 to AC terminals 128, or it steps the voltage at the DC terminals of inverter 132 down / up to supply the appropriate voltage at electrical energy storage device 108 when supplying energy from AC terminals 128 to electrical energy storage device 108.

[0065] The compensated error signal at 440 in Fig. 4 for example, from grid frequency ripple rejector 112, is provided to bidirectional power converter block 104 to set the DC voltage ratio between the voltage at electrical energy storage device 108 and the voltage across grid ripple capacitance 134 at the DC terminals of inverter 132. Grid frequency ripple rejector 112 sets the DC voltage ratio while rejecting AC voltage and harmonics of the AC ripple potential appearing across grid ripple capacitance 134. This forces inverter AC current and harmonics flowing from / to the DC terminals of inverter 132 to flow through grid ripple capacitance 134 while rejecting the inverter AC current and harmonics from flowing through bidirectional power converter 104 and subsequently flowing through electrical energy storage device 108.

[0066] Startup controller 120 senses the voltage at electrical energy storage device 108 and at grid ripple capacitance 134 at the terminals of bidirectional power converter 104. Startup controller 120 uses this information to provide a ramp starting value, and to ramp the ramp control signal at 540 until it reaches the ramp control signal final value and a steady state operating condition for inverter 132. The ramp control signal at 540 is provided to grid frequency92557188 ripple rejector 112. Startup controller 120 is responsive to receiving a shutdown signal from fault protector 124 to return the ramp control signal at 540 to the ramp reinitialization value. The shutdown signal from fault protector 124 also causes bidirectional power converter block 104 to shut down. Fault protector 124 provides the shutdown signal in response to a shutdown input signal or shutdown source, which may be any one of multiple input signals from the inverter control system such as the examples shown in Fig. 6.

[0067] Ripple current canceller 136 receives a power level signal from the inverter control. This power level signal is used to determine how many bidirectional converter elements of bidirectional power converter 104 to activate. This activation allows fewer or more bidirectional converter elements to be switching to minimize or at least reduce energy loss in bidirectional power converter 104. Ripple current canceller 136 determines the phase shift between active bidirectional converter elements. Bidirectional power converter 104 receives this information from ripple current canceller 136 and activates the required number of bidirectional converter elements and generates phase shifted control signals for each element to minimize or at least reduce the sum of the switching frequency ripple currents that flow through electrical energy storage device 108 and through grid ripple capacitance 134.

[0068] This combination of functions defined in electrical energy storage interface 100 of Fig. 1 provides optimization or at least improvement of electrical energy storage life and performance in an inverter by matching the electrical energy storage device voltage to the inverter voltage, controlling the transition from initial voltages to a state of matched voltages, rejecting inverter AC voltage and harmonic ripple from flowing to / from the electrical energy storage device, cancelling switching rate ripple currents to minimize the switching rate ripple current that flows through the electrical energy storage device, and providing fault protection to prevent over-charging, over-discharging, over-temperature, and other conditions that could damage the electrical energy storage device.

[0069] Various features related to an electrical energy storage interface are described in detail above and shown in the drawings. The disclosed features are intended as illustrative examples, any of which may be provided, individually or in any of a number of combinations, in embodiments. Electrical energy storage interface 100 in Fig. 1, for example, is illustrative of an92557188 embodiment that includes several elements or components, whereas other embodiments may include additional, fewer, and / or different elements or components, interconnected in the same way as shown in Fig. 1, in a similar way, or in a different way.

[0070] As an example, according to an embodiment an electrical energy storage interface includes a bidirectional power converter (as shown at 104 in Fig. 1, for example), and a startup controller (as shown at 120 in Fig. 1, for example), coupled to the bidirectional power converter. This embodiment is one example of an embodiment that includes several, but not all, of the elements or components shown in Fig. 1.

[0071] The bidirectional power converter in this example may be as shown in Fig. 1 and described at least above, including first terminals (to the left of bidirectional power converter 104 in Fig. 1, for example) to be coupled to an electrical energy storage device (108 in Fig. 1, for example) and second terminals (to the right of bidirectional power converter 104 in Fig. 1, for example) to be coupled to an inverter (132 in Fig. 1, for example). The bidirectional power converter is configured or otherwise operable to scale voltage between a first voltage at the first terminals for the electrical energy storage device and a second voltage at the second terminals for the inverter. The startup controller is configured or otherwise operable to determine an initial operating condition for the bidirectional power converter based on a first sensed voltage of the electrical energy storage device and a second sensed voltage of the inverter, and also to control transitions between the initial operating condition and a steady state operating condition for the bidirectional power converter. The transitions include a transition from the initial operating condition to the steady state operating condition, and a transition to return to the initial operating condition from the steady state operating condition.

[0072] As shown by way of example in Fig. 2 and described at least above, a bidirectional power converter may include multiple bidirectional converter elements shown by way of example at 208-1 and 208-n, each coupled between first terminals (204 in Fig. 2, for example) and second terminals (228 in Fig. 2, for example), and a converter controller (224 in Fig. 2, for example), coupled to each of the bidirectional converter elements, that is configured or otherwise operable to control which of those bidirectional converter elements are active and to control switching in the active bidirectional converter elements. This control of which ones of92557188 the bidirectional converter elements are active and the switching in the active bidirectional converter elements is to scale the voltage between the first voltage (at 204 in Fig. 2, for example) and the second voltage (at 228 in Fig. 2, for example). Each bidirectional converter element may be as shown in Fig. 3, for example, but other implementations are possible.

[0073] Regarding the startup controller in the example above, the startup controller may be as shown in Fig. 5 in some embodiments, and be configured or otherwise operable to receive (from storage voltage sense element 516 for example) a first voltage sense signal representing the first sensed voltage and (from grid ripple capacitance voltage sense element 520 for example) a second voltage sense signal representing the second sensed voltage. The startup controller may also be configured or otherwise operable to determine the initial operating condition based on the received first voltage sense signal and the second voltage sense signal.

[0074] A startup controller may be further configured or otherwise operable to receive a charging state signal, and to determine the initial operating condition responsive to the charging state signal indicating a predetermined charging state. Examples of such a charging state signal are shown at 508 and 528 in Fig. 5, and examples of charging states responsive to which an initial operating condition may be determined are provided elsewhere herein at least with reference to Fig. 5 and operation of initial conditions controller 532. There may be multiple charging state signals as shown by way of example in Fig. 5, and an initial operating condition may be determined responsive to one or more of those charging state signals indicating a respective predetermined charging state. The predetermined charging state that initiates or triggers initial operating condition determination may be the same, similar, or different for different charging state signals.

[0075] The example shown in Fig. 5 is illustrative of a startup controller that includes an initial conditions controller 532 and a ramp rate and trajectory controller 536 coupled to the initial conditions controller. The initial conditions controller 532 is configured or otherwise operable to determine the initial operating condition. The ramp rate and trajectory controller 536 is configured or otherwise operable to receive the determined initial operating condition from the initial conditions controller 532 and to control the transitions between the initial operating condition and the steady state operating condition.92557188

[0076] In the example above, an electrical energy storage interface includes a bidirectional power converter and a startup controller. Other embodiments may include other components or elements or provide other features, such as fault protection. In some embodiments, an electrical energy storage interface includes a fault protector, shown by way of example in Fig. 1 at 124 as being coupled to bidirectional power converter 104 and to startup controller 120, to generate a shutdown signal responsive to an input signal indicating a fault condition. Multiple fault conditions may be monitored in some embodiments, and in such embodiments a fault protector may be configured or otherwise be operable to generate a shutdown signal responsive to any of a number of input signals indicating a fault condition. Multiple fault condition monitoring is consistent with the example shown in Fig. 6, which illustrates one possible implementation of a fault protector.

[0077] Examples of input signals for fault condition monitoring are also provided herein. Any one or more of these input signals, and / or others that may be used to indicate a fault condition, may be among the input signals based upon which a fault protector generates a shutdown signal. In Fig. 6 the illustrated examples include the following, and embodiments may support shutdown signal generation based on any one or more of these examples (and / or others): an inverter shutdown request signal as shown at 608, to indicate a shutdown request from the inverter; an electrical energy storage device discharging over-current signal as shown at 612, to indicate an over-current condition of the electrical energy storage device during discharging; an electrical energy storage device charging over-current signal as shown at 616, to indicate an over-current condition of the electrical energy storage device during charging; an electrical energy storage device over-temperature signal as shown at 620, to indicate an over-temperature condition of the electrical energy storage device; an electrical energy storage device undervoltage signal as shown at 624, to indicate an under-voltage condition of the electrical energy storage device; an electrical energy storage device over-voltage signal as shown at 628, to indicate an over-voltage condition of the electrical energy storage device.

[0078] A fault protector may be further configured or otherwise be operable to receive a shutdown reset signal, as shown by way of example at 604, and to reset the shutdown signal responsive to receiving the shutdown reset signal.92557188

[0079] In embodiments that support a shutdown signal, which may be generated by a fault protector or in some other way, a bidirectional power converter may be further configured or otherwise be operable to receive the shutdown signal, and to shut down responsive to receiving the shutdown signal. Shutting down the bidirectional power converter under a fault condition protects the electrical energy storage device against damage from the fault condition, and may protect other components or elements such as the inverter and the bidirectional power converter from damage as well. Such a shutdown feature may provide at least some degree of fault protection for any of the components or elements in Fig. 1, for example.

[0080] As shown by way of example in Fig. 5, a startup controller may be configured or otherwise be operable to receive the shutdown signal (from the fault protector 124 in Fig. 1, for example), and to perform one or more actions responsive to receiving the shutdown signal. For example, an action may be to determine, after receiving the shutdown signal, a new initial operating condition for the bidirectional power converter based on a new first sensed voltage of the electrical energy storage device and a new second sensed voltage of the inverter. Another example of an action that may also or instead be performed is to transition from the steady state operating condition to the initial operating condition responsive to receiving the shutdown signal. These actions are described in further detail at least above, and performing these actions may involve any of such details that are described elsewhere herein.

[0081] A grid frequency ripple rejector may be provided in some embodiments, as shown by way of example in Fig. 1. An electrical energy storage interface such as the example interface 100 may include a grid frequency ripple rejector (112 in Fig. 1, for example), through which the startup controller (120 in Fig. 1, for example) is coupled to bidirectional power converter (104 in Fig. 1, for example). A grid frequency ripple rejector is configured or otherwise is operable to generate an error signal for control of the bidirectional power converter. Fig. 4 illustrates an embodiment in which the error signal is generated based on a difference between: (i) a product of the first sensed voltage and an output of the startup controller (generated and output by multiplier 444 in the example shown); and (ii) the second sensed voltage wherein grid frequency and harmonics components are reduced (output by inverter AC voltage and harmonic rejector 428 in the example shown). The component (ii) referenced in this example may also be described as the92557188 second sensed voltage with reduced grid frequency and harmonics components, or the second sensed voltage from which (or in which) grid frequency and harmonics components are reduced, for example.

[0082] The error signal is a compensated error signal in some embodiments, and as shown by way of example in Fig. 4, a grid frequency ripple rejector (or more generally an electrical energy storage interface) may include a compensated error generator (436 in Fig. 4, for example). A compensated error generator may be configured or otherwise operable to receive a difference signal (and in particular is coupled to receive the difference signal from difference block 432 in the example shown in Fig. 4) that is the difference between components (i) and (ii) in an example above.

[0083] Ripple cancellation is another feature that may also or instead be provided in some embodiments, as shown by way of example in Fig. 1. An electrical energy storage interface may therefore include a ripple current canceller (136 in Fig. 1, for example), coupled to a bidirectional power converter (104 in Fig. 1, for example). A ripple current canceller is configured or otherwise operable to cancel switching rate ripple current generated by the bidirectional power converter. In some embodiments, for switching rate ripple current cancellation the ripple current canceller is configured or otherwise operable to generate a signal to control phases of switching in the bidirectional power converter.

[0084] A ripple current canceller that is consistent with the example shown in Fig. 7 is configured or otherwise is operable to receive a power level signal as an input signal (at 704) and to generate, as an output signal (at 716), a phase shift control signal to enable and control phases of bidirectional converter elements switching in the bidirectional power converter. As shown in Fig. 7, one embodiment of a ripple current canceller includes power level parser 708 coupled to receive the power level signal, and phase offset generator 712, coupled to the power level parser 708, to generate the phase shift control signal.

[0085] Considering ripple current cancellation in the context of a multi-element bidirectional power converter that includes multiple bidirectional converter elements (such as the example shown in Fig. 2) a ripple current canceller may be configured or otherwise operable to generate a signal to control the number (that is, how many) of the bidirectional converter92557188 elements that are active and respective phases of switching in the active bidirectional converter elements. Stated another way, this generated signal, which is also referred to herein as a phase shift control signal, indicates information of the respective phases and enable states of the elements. The respective phases may be indicated as phases or a phase shift, for example. As described at least above, the phase shift is equal to 360° / m where m is the number of active (also referred to herein as enabled) bidirectional converter elements. Such switching control may be referred to as controlling phases or controlling phase shifts.

[0086] In the examples above, a bidirectional power converter and a startup controller are core components of an electrical energy storage interface, and other components or elements may also be provided, individually or together. According to some embodiments, an interface may include these core components, and may also include any one or more of the following: a grid frequency ripple rejector; a fault protector; a ripple current canceller.

[0087] Other combinations of components or elements are also possible, and the present disclosure is not limited to any particular combination of disclosed components or elements, or to the specific example implementations of such components or elements that are shown in the drawings or otherwise disclosed by way of example herein.

[0088] Embodiments are described above primarily in the context of power circuits or components thereof. Method embodiments are also possible.

[0089] Fig. 8 illustrates an example method according to an embodiment. Method embodiments, like other embodiments herein, may include disclosed features individually or in any of a number of combinations. The example method 800 in Fig. 8 is illustrative of an embodiment that is consistent with features that may be provided in an electrical energy storage interface that includes a bidirectional power converter and a startup controller. Other method embodiments may include additional, fewer, and / or different features.92557188

[0090] The example method 800 involves determining, at 802, an initial operating condition for a bidirectional power converter. The bidirectional power converter includes first terminals to be coupled to an electrical energy storage device and second terminals to be coupled to an inverter, and is configured or otherwise is operable to scale voltage between a first voltage at the first terminals for the electrical energy storage device and a second voltage at the second terminals for the inverter. These features of such a power converter are described in further detail at least above.

[0091] As shown at 804, the example method 800 also involves controlling transitions between the initial operating condition and a steady state operating condition for the bidirectional power converter. The determining involves determining the initial operating condition for the bidirectional power converter based on a first sensed voltage of the electrical energy storage device and a second sensed voltage of the inverter. The transitions include a transition from the initial operating condition to the steady state operating condition, and a transition to return to the initial operating condition from the steady state operating condition.

[0092] The operations at 802 and 804 may be performed by a startup controller, for example. For completeness, steady state operation of the bidirectional power converter is also shown, at 806.

[0093] As disclosed elsewhere herein, a bidirectional power converter may include multiple bidirectional converter elements, with each of the bidirectional converter elements coupled between the first terminals and the second terminals of the bidirectional power converter. In conjunction with such bidirectional power converter elements, a method may involve controlling which of the bidirectional converter elements are active, and controlling switching in the active bidirectional converter elements to scale the voltage between the first voltage and the second voltage. These controlling at 804, the steady state operation at 806, or both, may involve controlling which of the bidirectional converter elements are active and / or controlling switching in the active bidirectional converter elements.

[0094] In some embodiments, a method may involve receiving a first voltage sense signal representing the first sensed voltage and a second voltage sense signal representing the second sensed voltage, in which case the determining at 802 may involve determining the initial92557188 operating condition based on the received first voltage sense signal and the second voltage sense signal. Element 810 in Fig. 8 is intended to represent receiving, or otherwise obtaining, voltage sense signal(s). A voltage sense signal may be received from a voltage sense element, such as 412 and / or 420 in Fig. 4 or 516 and / or 524 in Fig. 5, and accordingly a method may involve receiving the first and second voltage sense signals. A voltage sense element is configured or otherwise operable to sense a voltage and provide a voltage sense signal. This illustrates how a method may involve sensing voltages at the first and second terminals and providing the first and second voltage sense signals.

[0095] Some embodiments may include features related to one or more charging states. For example, a method may involve receiving a charging state signal, and the determining at 802 may then involve determining the initial operating condition responsive to the charging state signal indicating a predetermined charging state. Examples of a charging state signal are shown at 508 and 528 in Fig. 5, and examples of charging states responsive to which an initial operating condition may be determined are provided elsewhere herein. Multiple charging state signals may be involved, and the determining at 802 may be responsive to one or more of those charging state signals indicating a respective predetermined charging state.

[0096] Element 812 in Fig. 8 is intended to represent receiving, or otherwise obtaining, one or more charging state signal(s). Operation of the example startup controller in Fig. 5 involves receiving charging state signals at 508 and 528. However, in other embodiments a method may involve obtaining one or more charging state signals by measuring or otherwise determining charging state(s).

[0097] Shutdown features may also or instead be provided in some embodiments. For example, a method may involve generating a shutdown signal responsive to any of a plurality of input signals indicating a fault condition. Element 820 in Fig. 8 is intended to represent generating (in the case of detecting a shutdown condition for example) or receiving (in the case of a feature to take action responsive to a shutdown signal for example) a shutdown signal.

[0098] Examples of input signals based upon which a shutdown signal may be generated are provided elsewhere herein. In order to avoid further congestion in the drawings, such input signals are not shown in Fig. 8.92557188

[0099] Shutdown signal monitoring is shown at 830 in Fig. 8, and a method may involve shutting down the bidirectional power converter responsive to a shutdown signal. Element 832 is intended to represent receipt of a shutdown signal, or more generally occurrence of a shutdown condition. The return arrow from 832 to 804 is intended to illustrate the power converter transitioning from the steady state operating condition to the initial operating condition for possible subsequent power converter operation after shutdown.

[0100] In some embodiments, a method may involve receiving a shutdown reset signal, and element 822 in Fig. 8 is intended to represent generating (in the case of detecting a shutdown reset condition for example) or receiving (in the case of a feature to take action responsive to a shutdown reset signal for example) a shutdown reset signal. The monitoring shown at 830 in Fig.8 also includes monitoring for a shutdown reset signal. A method may involve resetting the shutdown signal as an operation at 834, for example, responsive to receiving the shutdown reset signal. An example of an action that may be performed responsive to a shutdown reset signal, or more generally after a shutdown signal is generated or when a shutdown condition is cleared or no longer active, may include determining a new initial operating condition for the bidirectional power converter (at 802), based on a new first sensed voltage of the electrical energy storage device and a new second sensed voltage of the inverter. This is illustrated in Fig. 8 by the return arrow from 834 to 802. Another action that may also or instead be performed is transitioning from the steady state operating condition to the initial operating condition, as illustrated by the return arrow from 834 to 804. These actions are described in further detail at least above, and performing these actions may involve any of such details that are described elsewhere herein.

[0101] Grid frequency ripple rejection may be provided in some embodiments. For example, a method may involve generating an error signal for control of the bidirectional power converter. The error signal may be generated based on a difference between: (i) a product of the first sensed voltage and a transition control signal; and (ii) the second sensed voltage wherein grid frequency and harmonics components are reduced. Generation of such an error control signal is discussed in more detail at least above, in the context of an output of the startup controller as a transition control signal for component (i). Features described herein in the92557188 context of interface features or features of interface components or elements may also or instead be implemented in counterpart method steps, actions, or features.

[0102] As an example, generating the error signal may involve multiplying the first sensed voltage and the transition control signal (the ramp control signal in the example shown in Fig. 4) to generate component (i). Generating the error signal may also or instead involve reducing grid frequency and harmonics components in the second sensed voltage, and / or determining the difference between components (i) and (ii).

[0103] The error signal may be a compensated error signal, in which case a method may involve applying compensation (by applying a gain and / or low pass filtering for example) to the difference between components (i) and (ii).

[0104] Another feature that may be provided in some embodiments is ripple cancellation. A method may involve cancelling switching rate ripple current generated by the bidirectional power converter, for example by generating a signal to control phases of switching in the bidirectional power converter. In an embodiment, cancelling switching rate ripple current involves receiving a power level signal as an input signal (at 704 in Fig. 7, for example) and generating, as an output signal (at 716 in Fig. 7, for example), a phase shift control signal to control phases of switching in the bidirectional power converter.

[0105] For a multi-element bidirectional power converter that includes multiple bidirectional converter elements (such as the example shown in Fig. 2) ripple current cancellation (referenced at least above as cancelling switching rate ripple current generated by the bidirectional power converter), may involve generating a signal to control a number of the bidirectional converter elements that are active and respective phases of switching in the active bidirectional converter elements. Examples related to such a control signal and switching phase control are provided at least above, and may be provided in method embodiments.

[0106] Not all the features referenced in the method examples herein are explicitly shown in Fig. 8, in an effort to avoid further congestion in the drawing. Many of these features may be within the context of controlling transitions at 804 and / or steady state operation at 806.92557188

[0107] Fig. 8 illustrates an example method. The illustrated operations may be provided or supported in any of various ways, and other embodiments may include fewer, additional, and / or different operations or features, performed in a similar or different order. At least some variations to the example method shown in Fig. 8 may be or become apparent, for example, from features that are disclosed above, with reference to any of Figs. 1-7 and apparatus embodiments.

[0108] What has been described is merely illustrative of the application of principles of embodiments of the present disclosure. Other arrangements and methods can be implemented by those skilled in the art.

[0109] For example, embodiments need not include all elements or components that are shown in the drawings or described herein. Embodiments may include additional, fewer, and / or different components or elements.

[0110] It should also be appreciated that features disclosed herein in the context of a particular embodiment, such as an apparatus embodiment, are not limited only to that embodiment. Features may also or instead be implemented in other embodiments, such as a method embodiment. Similarly, method features may also or instead be implemented, supported, or otherwise provided in apparatus embodiments.

[0111] In addition, although described primarily in the context of methods and apparatus such as power circuits, other implementations are also contemplated, as instructions stored on a non-transitory computer-readable medium, for example.

Claims

92557188CLAIMS:

1. An electrical energy storage interface comprising: a bidirectional power converter, comprising first terminals to be coupled to an electrical energy storage device and second terminals to be coupled to an inverter, to scale voltage between a first voltage at the first terminals for the electrical energy storage device and a second voltage at the second terminals for the inverter; a startup controller, coupled to the bidirectional power converter, to determine an initial operating condition for the bidirectional power converter based on a first sensed voltage of the electrical energy storage device and a second sensed voltage of the inverter, and to control transitions between the initial operating condition and a steady state operating condition for the bidirectional power converter, wherein the transitions comprise: a transition from the initial operating condition to the steady state operating condition; and a transition to return to the initial operating condition from the steady state operating condition.

2. The electrical energy storage interface of claim 1, wherein the bidirectional power converter comprises: a plurality of bidirectional converter elements, each coupled between the first terminals and the second terminals; a converter controller, coupled to each of the bidirectional converter elements, to control which of the bidirectional converter elements are active and to control switching in the active bidirectional converter elements to scale the voltage between the first voltage and the second voltage.925571883. The electrical energy storage interface of claim 1 or claim 2, wherein the startup controller is configured to receive a first voltage sense signal representing the first sensed voltage and a second voltage sense signal representing the second sensed voltage, and to determine the initial operating condition based on the received first voltage sense signal and the second voltage sense signal.

4. The electrical energy storage interface of claim 3, wherein the startup controller is further configured to receive a charging state signal, and to determine the initial operating condition responsive to the charging state signal indicating a predetermined charging state.

5. The electrical energy storage interface of claim 3 or claim 4, wherein the startup controller comprises: an initial conditions controller to determine the initial operating condition; a ramp rate and trajectory controller, coupled to the initial conditions controller, to receive the determined initial operating condition from the initial conditions controller and to control the transitions between the initial operating condition and the steady state operating condition.

6. The electrical energy storage interface of any one of claims 1 to 5, further comprising: a fault protector, coupled to the bidirectional power converter and to the startup controller, to generate a shutdown signal responsive to any of a plurality of input signals indicating a fault condition.

7. The electrical energy storage interface of claim 6, wherein the plurality of input signals comprise any one or more of the following: an inverter shutdown request signal to indicate a shutdown request from the inverter; an electrical energy storage device discharging over-current signal to indicate an overcurrent condition of the electrical energy storage device during discharging;92557188 an electrical energy storage device charging over-current signal to indicate an overcurrent condition of the electrical energy storage device during charging; an electrical energy storage device over-temperature signal to indicate an overtemperature condition of the electrical energy storage device; an electrical energy storage device under-voltage signal to indicate an under-voltage condition of the electrical energy storage device; an electrical energy storage device over-voltage signal to indicate an over-voltage condition of the electrical energy storage device.

8. The electrical energy storage interface of claim 6 or claim 7, wherein the fault protector is further configured to receive a shutdown reset signal, and to reset the shutdown signal responsive to receiving the shutdown reset signal.

9. The electrical energy storage interface of any one of claims 6 to 8, wherein the bidirectional power converter is further configured to receive the shutdown signal, and to shut down responsive to receiving the shutdown signal.

10. The electrical energy storage interface of any one of claims 6 to 9, wherein the startup controller is further configured to receive the shutdown signal, and to: determine, after receiving the shutdown signal, a new initial operating condition for the bidirectional power converter based on a new first sensed voltage of the electrical energy storage device and a new second sensed voltage of the inverter; and / or transition from the steady state operating condition to the initial operating condition responsive to receiving the shutdown signal.

11. The electrical energy storage interface of any one of claims 1 to 10, further comprising: a grid frequency ripple rejector, through which the startup controller is coupled to the bidirectional power converter, to generate an error signal for control of the bidirectional power92557188 converter based on a difference between: (i) a product of the first sensed voltage and an output of the startup controller; and (ii) the second sensed voltage wherein grid frequency and harmonics components are reduced.

12. The electrical energy storage interface of claim 11, wherein the error signal is a compensated error signal.

13. The electrical energy storage interface of any one of claims 1 to 12, further comprising: a ripple current canceller, coupled to the bidirectional power converter, to cancel switching rate ripple current generated by the bidirectional power converter.

14. The electrical energy storage interface of claim 13, wherein the ripple current canceller is configured to generate a signal to control phases of switching in the bidirectional power converter.

15. The electrical energy storage interface of claim 2, further comprising: a ripple current canceller, coupled to the bidirectional power converter, to cancel switching rate ripple current generated by the bidirectional power converter, wherein the ripple current canceller is configured to generate a signal to control the number of the bidirectional converter elements that are active and respective phases of switching in the active bidirectional converter elements.

16. A method comprising: determining an initial operating condition for a bidirectional power converter that comprises first terminals to be coupled to an electrical energy storage device and second terminals to be coupled to an inverter, and that is operable to scale voltage between a first voltage at the first terminals for the electrical energy storage device and a second voltage at the second terminals for the inverter; controlling transitions between the initial operating condition and a steady state operating condition for the bidirectional power converter,92557188 wherein the determining comprises determining the initial operating condition for the bidirectional power converter based on a first sensed voltage of the electrical energy storage device and a second sensed voltage of the inverter; wherein the transitions comprise: a transition from the initial operating condition to the steady state operating condition; and a transition to return to the initial operating condition from the steady state operating condition.

17. The method of claim 16, wherein the bidirectional power converter comprises a plurality of bidirectional converter elements, each coupled between the first terminals and the second terminals, the method further comprising: controlling which of the bidirectional converter elements are active; controlling switching in the active bidirectional converter elements to scale the voltage between the first voltage and the second voltage.

18. The method of claim 16 or claim 17, further comprising: receiving a first voltage sense signal representing the first sensed voltage and a second voltage sense signal representing the second sensed voltage, wherein the determining comprises determining the initial operating condition based on the received first voltage sense signal and the second voltage sense signal.

19. The method of claim 18, further comprising: receiving a charging state signal,92557188 wherein the determining comprises determining the initial operating condition responsive to the charging state signal indicating a predetermined charging state.

20. The method of any one of claims 16 to 19, further comprising: generating a shutdown signal responsive to any of a plurality of input signals indicating a fault condition.

21. The method of claim 20, wherein the plurality of input signals comprise any one or more of the following: an inverter shutdown request signal to indicate a shutdown request from the inverter; an electrical energy storage device discharging over-current signal to indicate an overcurrent condition of the electrical energy storage device during discharging; an electrical energy storage device charging over-current signal to indicate an overcurrent condition of the electrical energy storage device during charging; an electrical energy storage device over-temperature signal to indicate an overtemperature condition of the electrical energy storage device; an electrical energy storage device under-voltage signal to indicate an under-voltage condition of the electrical energy storage device; an electrical energy storage device over-voltage signal to indicate an over-voltage condition of the electrical energy storage device.

22. The method of claim 20 or claim 21, further comprising: receiving a shutdown reset signal; resetting the shutdown signal responsive to receiving the shutdown reset signal.

23. The method of any one of claims 20 to 22, further comprising: shutting down the bidirectional power converter responsive to the shutdown signal.9255718824. The method of any one of claims 20 to 23, further comprising: determining, after generating the shutdown signal, a new initial operating condition for the bidirectional power converter based on a new first sensed voltage of the electrical energy storage device and a new second sensed voltage of the inverter; and / or transitioning from the steady state operating condition to the initial operating condition responsive to the shutdown signal.

25. The method of any one of claims 16 to 24, further comprising: generating an error signal for control of the bidirectional power converter based on a difference between: (i) a product of the first sensed voltage and a transition control signal; and (ii) the second sensed voltage wherein grid frequency and harmonics components are reduced.

26. The method of claim 25, wherein the error signal is a compensated error signal.

27. The method of any one of claims 16 to 26, further comprising: cancelling switching rate ripple current generated by the bidirectional power converter.

28. The method of claim 27, wherein cancelling the switching rate ripple current comprises generating a signal to control phases of switching in the bidirectional power converter.

29. The method of claim 27, further comprising: cancelling switching rate ripple current generated by the bidirectional power converter, wherein cancelling the switching rate ripple current comprises generating a signal to control a number of the bidirectional converter elements that are active and respective phases of switching in the active bidirectional converter elements.

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