KR20110104525A - Energy conversion systems with power control - Google Patents

Abstract

In one embodiment, the power conversion system includes a converter that induces a power stage to control power to or from the energy storage device. In another embodiment, the power conversion system includes a push-pull stage and an energy storage device that follows the push-pull stage. In another embodiment, an integrated circuit includes a power control circuit that provides power control to a power converter, and a power switch coupled to the power control circuit to operate the power converter. In another embodiment, the power conversion system includes two or more power converters with power control.

Description

Energy conversion system with power control {ENERGY CONVERSION SYSTEMS WITH POWER CONTROL}

This application is a partial continuing application of US Patent Application No. 12 / 340,715, filed December 20, 2008, which is incorporated by reference. This application claims priority from US patent provisional application 61 / 149,305, filed February 2, 2009, which is incorporated by reference.

Power converters are used to convert power from one form to another, for example converting direct current (DC) power to alternating current (AC) power. One important application in power converters is in transferring power from energy sources such as solar panels, batteries, fuel cells and the like to power distribution systems such as local and regional power grids. Most power grids operate on AC current at a line (or main) frequency of 50 to 60 cycles per second (hertz or Hz). In an AC grid, power flows in a pulsating fashion with a power peak that occurs at twice the line frequency: 100 Hz or 120 Hz. In contrast, many energy sources supply DC power in a fixed manner. Thus, a power converter system that transfers power from a DC source to an AC grid typically includes some form of energy accumulation to coordinate fixed input power with pulsating output power.

This can be better understood with reference to FIG. 1, which shows a mismatch between the DC power source and the 60 Hz AC load. The maximum amount of power available from the DC source is indicated as a constant value. Conversely, the amount of power that must be delivered to the AC load flows from zero to a maximum and drops to a minimum once every 8.33 milliseconds (ms). During T1, the power available from the DC source exceeds the instantaneous power required by the AC load. However, during T2, the maximum power available from the DC source is less than that required by the load. Thus, in order to effectively transfer power from the source to the load, the power converter system stores excess energy from the power source during T1 (shown in hatched area S), and stores the stored energy during T2 (shown in hatched area D). Should be discharged to the rod.

Energy storage devices for power converters tend to be expensive, bulky, less reliable, and inefficient. These factors are barriers to the large-scale adoption of alternative energy sources such as solar and fuel cells that generate electricity in the form of DC power. In addition, they are barriers to large-scale adoption of backup power systems for computers, homes, schools, businesses, and the like.

In solar energy systems, cost and reliability factors are particularly important. Solar panel manufacturers have increased the reliability of their products in that a 20-year warranty is common. However, manufacturers of power converters have not reached that they can provide a warranty period equivalent to that of solar panels.

1 shows a mismatch between a DC power source and a 60 Hz AC load in a power converter.
2 shows a conventional system for converting DC power from a solar (PV) panel to AC power.
3 shows power loss versus ripple voltage in a PV panel.
4 shows the cost versus capacitance for a capacitor.
5 shows the operation of a PV power converter system.
6 illustrates the operation of a power converter system for constant power control in accordance with some inventive principles of this patent disclosure.
7 illustrates an embodiment of a power converter system for constant power control in accordance with some inventive principles of this patent disclosure.
8 illustrates another embodiment of a power converter system in accordance with some inventive principles of this patent disclosure.
9 illustrates another embodiment of a power converter system for constant power control in accordance with some inventive principles of this patent disclosure.
10 illustrates an embodiment of a controller for performing positive power control in accordance with some inventive principles of this patent disclosure.
11 illustrates an embodiment of a power converter system in accordance with some inventive principles of this patent disclosure.
12 is a schematic diagram of an embodiment of a main power path suitable for implementing the inverter system of FIG. 11 in accordance with some inventive principles of this patent disclosure.
13-16 illustrate embodiments of PV panels in accordance with some inventive principles of this patent disclosure.
FIG. 17 shows the immediate demand for voltage from an H-bridge type DC / AC inverter compared to the voltage available from a DC link capacitor maintained at a fixed voltage.
18 shows the voltage from an H-bridge type DC / AC inverter compared to the voltage available from a DC link capacitor with a large AC voltage swing due to the constant power control feature in accordance with some inventive principles of this patent disclosure. Illustrates the immediate demand for
19 illustrates an embodiment of a power converter system with harmonic distortion mitigation, in accordance with some inventive principles of this patent disclosure.
20 illustrates an embodiment of a distortion mitigation system in accordance with some inventive principles of this patent disclosure.
21 shows another embodiment of a distortion mitigation system showing details of some exemplary implementations in accordance with some inventive principles of this patent disclosure.
22 illustrates another embodiment of a controller with harmonic distortion mitigation in accordance with some inventive principles of this patent disclosure.
23 illustrates an embodiment of grid current control in accordance with some inventive principles of this patent disclosure.
24 illustrates an embodiment of a controller in accordance with some inventive principles of this patent disclosure.
25 illustrates an embodiment of a controller with predistortion in accordance with some inventive principles of this patent disclosure.
26-29 illustrate embodiments of predistortion elements in accordance with some inventive principles of this patent disclosure.
30 illustrates an embodiment of impedance conversion in accordance with some inventive principles of this patent disclosure.
31 illustrates operation of a power conversion system without impedance conversion.
32 shows the voltage-current curves and power curves of a typical PV panel.
33 shows VI and power curves for a power source with one or more local maximum power points.
34 illustrates an embodiment of a power conversion system with constant power control and input sweeping characteristics in accordance with some inventive principles of this patent disclosure.
FIG. 35 illustrates an embodiment of the power conversion system in FIG. 20 wherein static power control is not possible in accordance with some inventive principles of this patent disclosure.
36 shows how the embodiment of FIGS. 20 and 21 operate under some conditions.
37 illustrates an embodiment of a system with multiple power sources in accordance with some inventive principles of this patent disclosure.
FIG. 37 illustrates an embodiment of a power conversion system in which multiple DC / DC converters include a positive power control function in accordance with some inventive principles of this patent disclosure.
FIG. 38 illustrates an embodiment of a power conversion system in which a plurality of DC / DC converters in accordance with the principles of some inventions of this patent disclosure include a positive power control function.
39-42 illustrate embodiments of a power conversion system including a plurality of converters having a power source and a central inverter in accordance with principles of some inventions of this patent disclosure.
43-51 illustrate embodiments that include distortion mitigation in accordance with the principles of some inventions of this patent disclosure.
FIG. 52 illustrates an embodiment of a power conversion system including EMI mitigation in accordance with principles of some inventions of this patent disclosure.
53 illustrates an embodiment of a power conversion system in accordance with principles of some inventions of this patent disclosure.

2 shows a conventional system for converting DC power from a solar (PV) panel to AC power. The PV panel 10 generates a DC output current I _PV at a typical voltage V _PV of approximately 20 volts, but panels with other output voltages can be used. DC / DC converter 12 increases V _PV to a link voltage V _DC of several hundred volts. The DC / AC inverter 14 converts the DC link voltage into the AC output voltage V _GRID . In this example, the output is assumed to be 120 VAC at 60 Hz to facilitate connection to the local voltage grid, although other voltages and frequencies may be used.

The system of FIG. 2 also includes a DC link capacitor C _DC and a decoupling capacitor C ₁ . One or both of these capacitors may perform an energy storage function to match the nominal normal power flow from the PV panel with the variable power requirements of the grid. The power pulses in the system come from the DC / AC inverter 14, which must deliver power to the grid at 120 Hz pulses. In the absence of a substantial energy storage device, these current pulses continue to be delivered to the PV panel, which appears as a variation (or 'ripple') in the panel voltage V _PV and / or current I _PV . Thus, the DC link capacitor C _DC or less, the decoupling capacitor C ₁ is used to reduce the ripple in the PV panel to an acceptable level and to store enough energy on a cycle basis.

In conventional systems, however, energy storage capacitors tend to be problematic components for some reasons. First, because other large capacitors are usually extremely expensive, capacitors large enough to provide adequate energy storage should generally be of electrolytic type. This can be better understood in the context of a system example designed to convert 210 watts, the input voltage from a PV panel, from 60 Hz to 120 VAC. The energy storage ΔE required to balance power based on cycle units is given by:

Where P is the power in watts (W), ω is the angular frequency of the AC sine wave with sec ⁻¹ units, and the energy storage ΔE has units of joules (J). At 60 Hz, ω = 120π, accordingly,

to be.

The amount of energy stored in the capacitor is given by equation (3).

Where C is the capacitance in Farads.

Assuming that the energy storage function is performed on the DC link capacitor C _DC and the DC link voltage has a 5 volt peak-to-peak swing at the top of the 495 volt DC level, the solution for capacitance gives the following results:

120 microfarad capacitors at sufficiently high rated voltages typically should be electrolytic capacitors, since ceramic capacitors of this size are usually extremely expensive.

The use of decoupling capacitor C ₁ for energy storage is typically worse. Since the voltage multiplication from the input voltage V _PV to the link voltage V _DC is about 25 to 1, the 5 volt peak-to-peak ripple for the DC link is equal to 0.2 volt ripple for the decoupling capacitor. Solving again for capacitance yields the following equation:

75 mF (75,000 microfarad) capacitors almost certainly need to be of electrolytic type.

However, electrolytic capacitors have a limited lifetime and tend to have high failure rates. As a further problem, the capacitance of electrolytic capacitors decreases over the entire life as the electrolyte dissipates and / or worsens, thus reducing efficiency and changing the dynamics of the overall system. In addition, electrolytic capacitors tend to be bulky, heavy and brittle, and have a large equivalent series resistance (ESR).

Apart from the above equations, it is advantageous to perform the energy storage function in the DC link capacitors rather than the decoupling capacitors since they generally reduce the size required in the capacitors. In general, it is more economical to store energy in the form of higher voltages on smaller capacitors than on lower capacitors on larger capacitors. However, even in conventional systems that store energy in DC links, capacitors were expensive, bulky, and unreliable components that often formed the weakest link in power converter systems.

Moreover, determining the size of an energy storage capacitor in conventional systems presents some difficult tradeoffs. For example, even with large capacitors, a certain amount of ripple still remains in the PV current and / or voltage. As shown in Fig. 3, even small amounts of ripple cause sufficient power loss to reduce the efficiency of the system. Ripple can be reduced by using larger capacitors, but as shown in FIG. 4, increasing the size of the capacitor dramatically increases the cost.

Power control

Some inventive principles of this patent post relate to a power control technique that fundamentally changes the dynamics of an interface between a power converter and a power source. Some of these principles relate to maintaining controlled impedance in consideration of power converters. Referring to FIG. 5, the PV panel can be designed as a voltage source V _PV and a series resistor R _PV . The system includes a variable resistor R ₁ which is controlled such that the impedance Z _{1 N} is always maintained in consideration of the power converter irrespective of the current I ₁ transmitted from the PV panel to the power converter. In one embodiment, the variable resistor R ₁ , as shown in FIG. 6, has an input voltage V ₁ and a reference voltage V _REF. It can be controlled by making the difference between the mulling.

Some inventive principles include the relationship between impedance control and energy storage functionality in a power converter. For example, in the embodiment of FIG. 7, the impedance Z _IN is maintained at a controlled value in consideration of the first power converter stage 18. One or more energy storage devices 20 balance the instantaneous input power from power source 16 with the instantaneous output voltage, which may flow over one or more next power stages. Power source 16 may include a PV panel, a fuel cell, a battery, a wind turbine, and the like. The first stage 18 may include one or more DC / DC converters, DC / AC inverters, rectifiers, and the like. The energy storage device may include one or more capacitors, inductors, and the like. The next stages may include one or more DC / DC converters, DC / AC inverters, rectifiers, and the like.

In one exemplary embodiment, the power source 16 comprises a PV panel, the first stage 18 comprises a DC / DC converter, and the energy storage device comprises a link capacitor. The impedance Z _IN taking into account the first power converter stage remains constant, while the voltage on the link capacitor is allowed to vary in response to the pulsating power demand of the next stage. Since input impedance control isolates the PV panel from the link capacitor, the voltage swing on the link capacitor can be much larger than in a system without impedance control. Since the amount of energy stored in the capacitor is directly related to the voltage swing across the capacitor, the size of the link capacitor can be reduced accordingly. It is also possible to eliminate or reduce the size of the decoupling capacitor at the input.

8 illustrates another embodiment of a power converter system in accordance with some inventive principles of this patent disclosure. The system of FIG. 8 receives power from a photovoltaic cell in a PV panel 22. The system includes a DC / DC converter 24, a link capacitor C _DC , a DC / AC inverter 26 and a controller 28. DC / DC converters are ones such as buck converters, boost converters, push-pull stages, rectifiers, etc., arranged like pre-regulators, main stages, etc. The above stage may be included. For purposes of illustration, it is assumed in this example that the DC / DC converter has a pre-regulator stage 24a next by the main stage 24b, but the principles of the invention are not limited to such an arrangement. DC / AC inverter 26 may include any suitable inverter topology, such as H-bridges, resonant inverters, and the like. The voltage and current sensors 30 and 32 provide the controller 28 with signals indicating the PV panel output voltage V _PV and the current I _PV , respectively. The controller outputs the drive signal D _l to control the pre-regulator.

The controller 28 controls the pre-regulator stage 24a in the DC / DC converter in such a way as to maintain the PV panel output voltage V _PV or current I _PV at a substantially constant value that eliminates or reduces input ripple. A positive power control loop (conceptually shown by arrow 34) is realized. This causes the PV panel to refer to a constant load essentially, which results in a constant power transfer. In essence, the constant power control loop isolates the PV panel from any stage after the pre-regulator 24a, so that the energy storage device or devices can be arranged downstream of the constant power control loop. . In the example of FIG. 8, the link capacitor is used for energy storage to provide cycle-by-cycle power balance at the AC output frequency. However, in other embodiments, the energy storage may be located between the pre-regulator and the main stage or any other additional stage downstream of the constant power control loop.

Because the positive power control loop isolates the power source from the downstream energy storage device, the energy storage device may be allowed to operate with a wider variation than would otherwise be acceptable. For example, capacitors can operate with greater voltage fluctuations and indicators can operate with greater current fluctuations. This, in turn, may enable the use of smaller energy storage devices.

Positive power control is distinguished from maximum power point tracking (MPPT) in accordance with some inventive principles of this patent disclosure, but may be used with it. While MPPT can determine the operating point that maximizes the power available from the power source under certain operating conditions, static power control can allow the system to maintain the operating point despite variations in load. For example, in some embodiments, the positive power control technique can be used to maintain the operating point, as described in more detail below with reference to FIG. 22, while the MTTP technique is used to find the operating point for the system. Can be used.

Regulating a constant DC input voltage or current can provide some advantages. Firstly, reducing ripple in the input waveform improves the efficiency of some DC power sources, such as PV panels, which are experiencing ripple-related resistive losses. Secondly, moving energy storage to DC link capacitors can eliminate the need for input electrolytic capacitors, which are expensive, bulky, and unreliable components with short lifespan. Instead, energy can be stored in the form of higher voltages for DC link capacitors that are less expensive, more reliable, longer-lived and take up less space. In addition, the size of the DC link capacitor itself can also be reduced.

In an exemplary embodiment as described above with respect to FIG. 8, the controller has one sense input (V _PV or I _PV ) and one output Dl that controls the pre-regulator at the DC / DC converter. That is, the positive power control loop is realized by controlling the first stage in the power path in response to the parameter sensed at the overall input of the power converter system.

Some other inventive principles of the present patent disclosure include controlling one or more power stages other than the first stage in response to sensed parameters anywhere in the system (1); And / or controlling 2 any power stage or stages corresponding to one or more parameters sensed anywhere in the system other than the entire input, thereby realizing positive power control.

For example, according to some of these other inventive principles, the embodiment of FIG. 8 controls controller 28 by controlling pre-regulator 24a in response to a sensed parameter at the output of DC / AC inverter 26. Can be modified to realize the home power control loop. As another example, the system of FIG. 8 can be modified such that the controller 28 realizes a positive power control loop by controlling the DC / AC inverter 26 in response to the input voltage V _pv .

9 illustrates another embodiment of a power converter system with constant power control in accordance with some inventive principles of this patent disclosure. Power pass 36 includes N power stages 38, where N = 1. The power pass receives power from the power source 40 and outputs power to the load 42. The controller 44 receives one or more sensing signals S ₁ , S _2... S _L from the power path, and outputs one or more driving signals D ₁ , D _{2 ...} D _{M on the} power path. The power stage 38 is one or more DC / DC converters, DC / AC inverters, rectifiers for processing power as converted from the form provided by the power source 40 to the form delivered to the load 42. It may include an energy storage device. One or more sense signals S ₁ , S _{2 ...} S _L may be taken from the input and / or output of any power stage, a point in the power stage, and / or a point between the power stages. One or more drive signals D ₁ , D _{2 ...} D _M may be arranged to control one, any or all power stages, or portions of a power stage. The drive signal can be arranged to control one drive stage or portions of one or more drive stages in unison.

The controller 44 uses a constant power control loop using at least one sense signal from one point other than the overall input to the power path, and / or at least one drive signal driving at least one power stage other than the first stage. To realize.

In some examples, providing constant power control may include maintaining a parameter at a constant value, such as maintaining the overall input voltage at a constant value in a power converter system. In another example, the constant power control may include controlling a parameter having dynamic characteristics, such as controlling an AC voltage swing on the link capacitor to have a sinusoidal waveform. In some embodiments, some stages may be left to be driven freely, such as uncontrolled, open loop, fixed pulse width PWM, etc., while in other embodiments, some form of closed loop control may be applied to all stages. Can be applied.

In some embodiments, constant power control may include regulating the value of one or more sensed parameters, such as regulating the value of the sensed input voltage at the input of the system. In some embodiments, the controller can use one or more additionally sensed parameters as a feedback signal, alone or in combination with other sensed parameters. In other embodiments, one or more additionally sensed parameters may be used alone or in combination with other sensed parameters as a feed forward signal.

In Figure 9, the power stages in the power pass are generally shown in line, but the stages need not be in series. At least one first stage is coupled to the overall input of the power path, but some stages may be arranged in series-parallel combination, or any other suitable shape, in parallel, in accordance with the principles of the invention.

Also, rather than directly regulating the input to invalidate the ripple, the ripple in an energy storage device other than the system can be controlled to produce the same effect at the input.

10 illustrates an embodiment of a controller for realizing positive power control in accordance with some inventive principles of this patent disclosure. The controller receives one or more sense signals S ₁ , S _2… S _L from one or more sense circuits, which can be simple resistance connections, current shunts, hall-effect sensors, bridge circuits, transformers, and the like. do. One or more amplifier / butter circuits 46 each comprise H ₁ (S), H ₂ (s) _... It may be used to adjust the sense signal before being applied to one or more control blocks 48 that realize the H _L (s) function.

The output from the control block is applied to a control algorithm section 50 that realizes one or more control algorithms to generate output drive signals D ₁ , D _{2 ...} D _M. One or more control blocks 48 and / or control algorithm sections 50 may be realized in hardware, software, firmware, or the like, or any combination thereof. The hardware can be realized with analog electrical circuitry, digital electrical network or any combination thereof.

11 illustrates an embodiment of a power converter system in accordance with some inventive principles of this patent disclosure. DC power is applied to the system at terminals 292 and 294. Although the embodiment of FIG. 11 is shown in the context of solar panel 290, it may be used for other DC power sources such as fuel cells, batteries, capacitors, and the like. In this example, the main power path leads to a collection of components that form the DC-DC converter 306. DC-DC converters are easily distributed to local users and / or transmitted to remote users via a power grid, etc., from the relatively low voltages and high currents characteristic of PV panels with crystalline cells and some other DC power sources. The DC power is varied with a relatively high voltage and low current suitable for converting AC power. In other embodiments, for example, in systems based on thin film PV cells, DC power is generated at higher voltages, thereby eliminating or reducing the need or utility of voltage rise, preregulation, and the like. In this embodiment, the DC-DC converter is shown in two stages, a boost type pre-regulator and a push-pull type main stage. However, in other embodiments, the DC-DC converter can be realized in any suitable arrangement of single or multiple stages.

Referring again to FIG. 11, a zero-ripple input filter 296, for example a passive filter, can be used to reduce high frequency (HF) ripple for improved efficiency. Depending on the implementation, the benefit of the zero ripple filter may not be worth the extra cost.

The pre-regulator 298 allows the system to operate from a wide range of input voltages to accommodate PV panels from other manufacturers. In addition, the pre-regulator may facilitate the implementation of advanced control loops, thereby reducing input ripple as discussed below. For example, the pre-regulator can be implemented as a high frequency (HF) boost stage with soft switching and compact size for high efficiency. In this example, the pre-regulator provides a small amount of initial voltage boost to supply to the next stage. However, other pre-regulator stages such as buck converters, buck-boost converters, push-pull converters and the like can be used as the pre-regulator stages.

Push-pull stage 300 provides a majority of the voltage boost with transformer 302 and rectifier 304. Since the drivers for both power switches can be at the same common voltage, the use of a push-pull stage can facilitate the implementation of the entire system with a single integrated circuit. The output from the rectifier stage 304 is applied to a DC link capacitor C _DC that provides a high voltage DC bus that feeds the DC-AC inverter stage 312.

Inverter stage 312 includes a high voltage output bridge 308, which in this embodiment is implemented as a simple H-bridge to provide single-phase AC power, but multi-phase embodiments may also be implemented. . The passive output filter 310 smoothes the waveform of the AC output before it is applied to the load or grid at the neutral and line output terminals L and N.

The first (input) PWM controller 314 controls the pre-regulator 296 in response to various sense inputs. In the embodiment of FIG. 11, voltage sensors 316 and 32 and current sensor 318 provide measurements of the overall input voltage and current and the output voltage of the pre-regulator, respectively. However, the first PWM controller can operate in response to fewer or more sense inputs. For example, any of these sense inputs may be omitted and / or the current measured at any other point along the voltage or power path to another sense input, such as DC link capacitor C _DC .

As noted above, power is preferably derived at a constant rate from the DC source, but the instantaneous AC power output varies twice the AC line frequency between zero and some maximum value. To prevent these AC power fluctuations from being reflected to the DC power source, the energy storage capacitors store energy while in the trough (or valley) in the AC line cycle, thereby saving energy while at the peak in the AC line cycle. Used to release. Conventionally, this has been realized through the use of large electrolytic capacitors for DC link capacitor C _DC , which are kept at relatively constant values with small amounts of ripple.

In some embodiments, the first PWM controller 314 controls the pre-regulator 296 to maintain a constant voltage at the input terminals 292 and 294, as shown above (and shown by arrow 315). Internal static power control loop is realized. If the power available from the PV panel is constant, maintaining a constant panel voltage, of course, results in a constant output current from the panel. Optionally, the controller can regulate current rather than voltage. The constant power control loop prevents ripple on the DC link capacitors from returning to the input. Thus, the voltage swing for the DC link capacitor can be increased and the size of the capacitor can be reduced, thereby enabling the use of capacitors that are more reliable, smaller, less expensive, and the like.

The maximum power point tracking (MPPT) circuit 344 forms an external control loop, so that the voltage and current sensors 316 and 318, respectively, at optimal points to maximize the output power available from the DC power source, which in this example is a PV panel. Maintain the average input voltage and current sensed by. The second (push-pull) PWM controller 324 controls the push-pull stage operating in a fixed duty cycle in this embodiment. Summing node 329 compares the DC link voltage from sensor 326 with the link reference voltage LINK REF and applies the output to link voltage control circuit 322. Optionally, the output of the summing node 329 may be applied to the third (output) PWM controller 330 to cause the output to control the link voltage.

The DC link voltage controller 322 can operate in other modes. In one mode, it may simply cause the output from the summing node 329 to be applied to the PWM circuitry so that the DC link voltage is regulated to a constant value. However, if used with the input ripple reduction loop discussed above, DC link voltage controller 322 can filter out AC ripple such that only the third PWM loop adjusts the long term DC value (eg, RMS value) of the DC link voltage. have. That is, the AC ripple for the DC link capacitor rides a DC pedestal that slides up and down in response to the DC link voltage controller. This may be useful, for example, to control distortion at the AC output voltage as discussed below.

The third (output) PWM controller 330 controls four switches in the H-bridge 308 to provide a sinusoidal AC output waveform. Non-DQ, non-cordic polar form digital phase locked loop (DPLL) 332 helps to synchronize the output PWM to the AC power line. The overall AC output is monitored and controlled by the grid current control loop 336 which adjusts the output from the MPPT circuit, the DC link voltage controller, the DPLL, and the third PWM controller 30 in response to the output voltage and / or current. do. The harmonic distortion mitigation circuit 338 also adjusts the output PWM via the summing circuit 334 to remove distortion in response to the output voltage and current waveforms sensed by the respective voltage and current sensors 340 and 342. Reduce. The output from the harmonic distortion mitigation circuit can further be applied to the grid current control loop 336.

The output signal from harmonic distortion mitigation circuit 338 may also be applied to the DC-link voltage controller for optimization of the DC-link voltage. In general, it is desirable to minimize the DC-link voltage to increase overall efficiency.

However, if the valley of voltage excursions drops too low on the DC-link capacitor, it may cause excessive distortion at the AC output. Thus, the DC-link voltage controller slides the DC pedestal up and down on the DC-link capacitor to keep the bottom of the AC valley at the lowest possible point, while maintaining distortion at an acceptable level as indicated by the harmonic distortion mitigation circuit. can do.

In some other embodiments, the DC-link voltage controller 322 can provide a feedback signal that is compared to the reference signal and applied to the second PWM controller 324, which adjusts the PWM to a push-pull stage to provide a DC link. The voltage can be controlled.

12 is a schematic diagram of an embodiment of a main power path suitable for realizing the inverter system of FIG. 11 in accordance with some inventive principles of the present patent disclosure. Power from DC power source 346 can be a large energy storage capacitor, or prevents HF switching transients from feeding back to the DC power source if an input ripple reduction control loop is used. Can be applied to the system at capacitor C ₁ , which can be a small filter capacitor. Inductor L1, transistor Q1 and diode D1 form a pre-regulation boost converter controlled by an input PWM controller.

The output from the boost converter appears across capacitor C2, which may provide HF filtering and / or energy storage, depending on the implementation. The push-pull stage includes transistors Q2 and Q3 that selectively drive the transformer in response to a push-pull PWM controller. The transformer may be split core type (T1, T2), single core type, or any other suitable configuration, as shown in FIG. The transformer has the appropriate turns ratio to properly feed the output bridge by generating a high voltage DC bus across the DC-link capacitor C _DC . Depending on the implementation, the transformer may also provide galvanic isolation between the input and the output of the inverter system. The rectifier may include passive diodes D2-D5, active synchronization rectifier, or any other suitable arrangement, as shown in FIG.

Transistors Q4-Q7 in the HV output bridge are controlled by an output PWM controller to generate an AC output that is filtered by grid filter 348 before being applied to a load or power grid.

An advantage of the embodiment of FIG. 12 is that it can be easily employed as an integrated power converter, for example with a single integrated circuit (IC). Since multiple power switches are referenced to a common power supply connection, isolated drives are not required for these switches. The combination of constant power control features with push-pull stages and downstream energy storage devices can be particularly beneficial due to the mutual synergy between the components. In addition, these benefits can be extended to individual implementations.

In a monolithic implementation of the overall structure, there may be electrical isolation between the high side switches and the corresponding low side switches in the output H-bridge. There may also be insulation between other parts of the system. For example, the sense circuit located in one section sends information to processing circuitry in another section that performs control and / or intercommunication and / or other functions in response to information received from the first section. Can be. Depending on the specific application and power handling requirements, all components, including power electronics, passive components and control circuits (intelligent) can be manufactured directly on the IC chip. In other embodiments, it may be desirable to have large passive components such as inductors, transformers, and capacitors located outside the chip. In yet another embodiment, the system of FIG. 12 can be implemented as a multi-chip solution.

Some further inventive principles of this patent disclosure relate to integrating positive power control functionality into a power source and / or power converter system. In some embodiments, the positive power control device may be integrated into a power source at a lower level, such as cell level, string level. For example, in the PV panel 350 as shown in FIG. 13, one or more positive power control loops 350 may be integrated into each cell 354 on the panel. In yet another embodiment as shown in FIG. 14, one or more positive power control loops 356 may be integrated into panel 358, each having a series of cells 360. In another embodiment as shown in FIG. 15, a single positive power control loop 362 can be used for the combined output from all cells on the panel 364. Single loop 362 may be integrated with one of cells 366 or may be separate from any cell. In yet another embodiment as shown in FIG. 16, multiple positive power control loops 368 may be associated with panel 370 either integrally or separately from the panel. In another example, the positive power control loop may be integrated with each cell as one or multiple individual components associated with each cell, or partially or fully integrated on the same substrate used for each cell. Integrated solutions of this type can include outputs from multiple positive power control loops that can be combined in series, parallel, series-parallel combinations, and the like.

Some further inventive principles of this patent disclosure relate to controlling power to a variable rather than constant value in a power converter system. For example, in some embodiments, power may be controlled by any function or specific function tailored to a particular system. In other embodiments, the power may be synchronized according to variations in the power demand of the load, variations in the power supplied by the source, a combination of the two, and the like.

Distortion Mitigation

Some further inventive principles of this patent disclosure relate to techniques for mitigating distortion, such as harmonic distortion in power converter systems. Although some principles relating to distortion mitigation are shown in the context of an embodiment that also includes constant power control, the principles of the invention relating to distortion mitigation can be applied independently to the principles of constant power control and other inventions disclosed herein. have.

FIG. 17 shows the immediate demand for voltage from an H-bridge type DC / AC inverter compared to the voltage available from a DC link capacitor maintained at a fixed voltage. As long as the DC link voltage remains above the peak voltage demand from the inverter (plus the extra amount for headroom), the inverter will produce an AC output with little harmonic distortion (HD) in the output voltage and current waveforms. Can be.

FIG. 18 shows the immediate demand for voltage from an H-bridge type DC / AC inverter compared to the voltage available from a DC link capacitor with a large AC voltage swing due to the positive power control feature as described herein. . In general, variations in the DC link voltage can cause distortion in the AC output. Also, at certain points in the line cycle, the minimum value in voltage available from the link capacitor matches the peak in voltage demand from the inverter. At these points, the AC output voltage and / or current from the inverter may be excessively distorted due to the lack of adequate voltage and headroom for the inverter. That is, in some embodiments, the inclusion of the constant power characteristic may cause a certain amount of distortion in the output current, depending on the amount of AC ripple allowed for the DC link capacitor. Harmonic distortion is particularly problematic for grid tie applications or any other application where regulation and / or specifications limit the amount of distortion at the AC output.

19 illustrates an embodiment of a power converter system with harmonic distortion mitigation, in accordance with some inventive principles of this patent disclosure. This embodiment includes a power path having a power source 52, a first power stage 54, an energy storage element 56, and a second power stage 58. Controller 60 imposes positive power control on the system using one or more sense inputs obtained from any suitable point in the system and one or more drive outputs applied to any suitable point in the system. Harmonic distortion mitigation (HDM) device 62 may utilize one or more sense inputs obtained from any suitable point in the system and one or more drive outputs applied to any suitable point in the system.

The harmonic distortion mitigation block may implement one or more many other mitigating powers, in accordance with some inventive principles of this patent disclosure. One example is shown in the embodiment of FIG. 11. As another example, the HDM block takes one or more sense inputs from the inputs and outputs of the second power stage 58, and in a similar manner to the HDM characteristics shown in the embodiment of FIG. 11, the first stage 54 and / or the like. Or control the second stage 58. The HDM function can be coordinated with the constant voltage control function or can operate independently of the constant voltage control.

20 illustrates an embodiment of a distortion mitigation system in accordance with some inventive principles of this patent disclosure. The embodiment of FIG. 20 includes a power path having an energy storage element 200, a power stage 202, and a rod 204. The controller 206 receives one or more load signals S _L that provide information about distortion to the load in the power flow. One or more control signals, for example one or more modulation signals S _M , allow the controller to control in such a way as to reduce the distortion of the power stage. One or more sense signals S _ES from the energy storage element provide information that can be used to control one or more parameters of the energy storage element. Although shown coupled to and from a specific point in FIG. 20, the signal may be combined at or from any other suitable point. For example, one or more load signals S _{L are} shown as originating between the power stage and the load, but they may be taken directly from the power stage, rod or any other suitable location.

The controller 206 is a control function such as a modulator 210 for controlling the power stage 202, a synchronization function 212 for synchronizing the modulator to the load, a distortion mitigating function for reducing distortion to the load in the power flow ( 208). Controller functions may be implemented in hardware, software, firmware or any combination thereof. The hardware can be realized in analog circuits, digital circuits or any combination thereof. The implementation of the function may be centralized on a single device or distributed across multiple devices and the like.

Energy storage element 200 may include one or more capacitors, inductors, or any other energy storage elements. The power stage 202 may include one or more DC / DC converters, DC / AC inverters, rectifiers, and the like. The rod can be an AC rod, a DC rod or any combination thereof. The control function may include any suitable type of modulation function, such as pulse width modulation (PWM), pulse frequency modulation (PFM), or any other suitable type of control or modulation function. Synchronization function 212 may include a phase locked loop (PLL) function, a delay locked loop (DLL) function, or any other suitable function to synchronize the control of the power stage with the load. Distortion mitigation function 209 may include harmonic distortion mitigation or elimination, or any other type of distortion mitigation.

21 shows another embodiment of a distortion mitigation system showing details of some exemplary implementations in accordance with some inventive principles of this patent disclosure. In the embodiment of FIG. 21, the energy storage element comprises a capacitor C _DC with a variable voltage, for example due to constant power control. The power stage 214 includes, in this embodiment, a DC / AC inverter that includes an H-bridge. The rod 216 may include any type of AC rod, but in this embodiment it is assumed to include a power distribution grid that operates on a conventional sinusoidal AC waveform. Grid filter 218 may be included between the H-bridge and the grid.

In this embodiment, the controller 207 receives the link voltage V _DC obtained from the capacitor C _DC by the voltage sensor or the connection 224. The PWM modulated signal ma2 is provided from the controller 207 to the H-bridge. The load signal includes a grid current I _G obtained from the current sensor or connection 222 and a grid voltage V _G obtained from the voltage sensor or connection 220.

The controller of FIG. 21 includes a sinusoidal PWM element 226 for generating a pulse width modulated signal Ma2 that causes the H-bridge to produce a sinusoidal AC output. Although the present embodiment has been described with respect to sine waveforms, other types of AC waveforms can be used in other embodiments. The synchronization function is performed by the digital phase-closed loop 228 which generates a phase signal [theta] in response to the grid voltage V _G. The distortion mitigation function is performed by a harmonic distortion cancellation (HDC) element 230 that generates a magnitude signal Ma in response to grid current I _G. The HDC element may optionally include a link voltage control function that operates in response to the link voltage V _G. The output from the HDC element and the DPLL is applied to a sinusoidal PWM element 226 that generates a modulated signal Ma2 for H-bridge control. The output from the HDC element and the DPLL can be applied directly to the sinusoidal PWM element 226 or through a combination of other elements. For example, in another embodiment, the signal Ma is not applied directly to the sinusoidal PWM element 226, but instead can be combined with the output of the sinusoidal PWM element with an adder.

The selection and arrangement of functions within the controller 207 can vary widely, in accordance with some inventive principles of this patent disclosure. Some embodiments are described by way of example below.

22 illustrates another embodiment of a controller with harmonic distortion mitigation in accordance with some inventive principles of this patent disclosure. In the embodiment of FIG. 21, the HDC element 230 includes a sinusoidal wave generator 234 that generates a sinusoidal signal sin (θ) in response to the phase signal [theta] from the DPLL. The signal sin (θ) is combined with the reference signal I _REF by the multiplier 236 and compared to the grid current I _G by the adder (or comparator) 238 to generate the error signal I _ERR . Generate _REF sin (θ). The error signal is likely to be applied to the transfer function H (s) by the function block 240 to generate an error magnitude signal MAG.

The embodiment of FIG. 22 realizes a direct method of controlling the power stage compared to the sinusoidal signal I _REF sin (θ) with the grid current multiplied. The output Ma2 obtained as a result from the sinusoidal PWM 226 has the form Ma2 = MAG * sin (θ). In operation, the MAG portion may exhibit distortion as a function of time when the control loop simply tries to maintain a sinusoidal output despite the ripple on the link voltage. The system's ability to mitigate harmonic distortion will depend on the bandwidth of the pass, which includes a comparator 238, a function 240, and a sinusoidal PWM 226, forming a loop with the H-bridge and grid filter. Can be. Such a loop will typically remove harmonics at frequencies below the bandwidth of the loop, such as lower magnitudes. Thus, a pass that includes a comparator, H (s) and a sinusoidal PWM will form a relatively fast inner loop, whereas a pass that includes a DPLL 228 and a sine generator 234 will form a slower outer loop.

The reference signal I _REF may be a fixed reference signal. Optionally, as shown in FIG. 22, I _REF may be provided by the DC link voltage control feature 242 as part of another control loop to control the DC link voltage. Average or RMS version of the link voltage V _DC, or V _DC may be compared to a reference signal V _REF to generate I _REF. DC link voltage control can be realized as another relatively slow outer control loop.

Some further inventive principles of this patent disclosure relate to grid current control. The embodiment of FIG. 23 includes a grid current control element 244 for generating a direct signal I _D and an orthogonal signal I _Q in correspondence with the phase signal θ from the DPLL as well as the grid current I _G , the reference signal I _REF2 . . The direct and quadrature signals are applied to the inverse DQ modifying element 246 which generates the phase signal φ applied to the sine generator 234 and the magnitude signal MAG 'applied to the sine PWM 226. Outputs from HDC block 230 and sine PWM 226 (MAG and MAG ") are each combined by adder 248 to provide the final modulated signal Ma2.

By providing grid current control, the embodiment of FIG. 23 can be configured such that grid voltage V _G and grid current I _G become closer in phase relationship. For example, the previous embodiment of FIG. 22 may provide proper operation in a system with purely or mostly resistive grid rods. In a system with an ineffective grid load, the grid current control characteristics of the embodiment of FIG. 23 can cause the grid voltage and current to be in phase, providing improved harmonic distortion rejection to the reactive grid.

Although shown with HDC characteristic 230 in FIG. 23, the grid current control technique disclosed herein may be implemented separately from this or any other HDC characteristic, in accordance with some inventive principles of this patent disclosure.

The grid current control technique shown in the context of FIG. 23 can also be combined in various forms of link voltage control. For example, either or both of reference signals I _REF1 and I _REF2 may be provided by one or more link voltage control elements, such as element 242 shown in FIG. 22.

Some further principles of this patent disclosure relate to the use of predistortion techniques for distortion mitigation. 24 shows a controller 250 having a control function, such as a modulator 210 for generating one or more control signals S _M for controlling the power stage, and load and output the output of the power stage in response to one or more load signals S _L. An embodiment of a synchronization function 212 is shown that synchronizes together. Predistortion element 252 provides some form of predistortion in response to any suitable signal, such as sense signal S _ES from the energy storage element. The pre-signal may be applied to one or more control signals S _M or any other signal or element to provide distortion mitigation. The controller function may be due to hardware, software, firmware, or the like or any combination thereof. The hardware can be realized in analog circuits, digital circuits or any combination thereof. The realization of such functions may be integrated into a single device or distributed across multiple devices.

25 illustrates an embodiment of a controller with predistortion, in accordance with some inventive principles of this patent disclosure. The modulated signal Ma may be provided by any suitable source, such as any Ma2 signal in the embodiments described above. In this embodiment, the modulation signal Ma is provided by a simple sine PWM element 258 controlled by the DPLL 260 in response to the grid voltage V _G. Predistortion element 254 generates a predistortion signal Ma 'coupled to modulator signal Ma by adder 256 to generate a final modulation signal Ma ". The final modulation signal Ma" is applied to any suitable power stage. Can be. In this embodiment, the power stage may be an H-bridge as shown in FIG. 21.

The predistortion method according to some inventive principles of this patent disclosure can be realized individually or in combination with the various types of distortion mitigation principles disclosed herein. Predistortion element 254 may realize any type of predistortion to mitigate or eliminate distortion from the power stage to the load in power flow. For example, when applied to the system of FIG. 21, predistortion 254 may generate a predistortion signal Ma ′ that predicts and compensates for distortion due to ripple on link voltage V _DC .

FIG. 26 illustrates an embodiment of a predistortion element, in accordance with some inventive principles of this patent disclosure. The embodiment of FIG. 26 includes a lookup table 262 for providing the predistortion signal Ma 'in response to the instantaneous link voltage V _DC and the average value of the link voltage V _{DC ( AVERAGE )} .

27 illustrates another embodiment of a predistortion element in accordance with some inventive principles of this patent disclosure. In the embodiment of FIG. 27, the predistortion signal Ma 'is generated by dividing the average value V _{DC ( AVERAGE )} of the link voltage by the instantaneous value V _DC . The result can be used directly as a predistortion signal or applied to further processing. For example, the result can be multiplied by the modulation signal Ma after conversion by the function f (s), as shown in FIG.

28 shows another embodiment of a predistortion element in accordance with some inventive principles of this patent disclosure. The embodiment of FIG. 28 provides a predistortion signal Ma 'in response to an instantaneous link voltage V _DC , an average value of the link voltage V _{DC ( AVERAGE )} , an instantaneous grid voltage V _G, and an RMS value V _{G ( RMS )} of the grid voltage. A lookup table 264.

29 illustrates another embodiment of a predistortion element in accordance with some inventive principles of this patent disclosure. The embodiment of FIG. 29 provides any suitable transfer function H (s) in response to the instantaneous link voltage V _DC , the average value of the link voltage VDC _{( AVERAGE )} , the instantaneous grid voltage V _G and the RMS value V _{G ( RMS )} of the grid voltage. The predistortion signal Ma 'is calculated accordingly.

In some applications, the embodiments shown in FIGS. 26 and 27 may provide adequate distortion mitigation when the grid load has a purely or nearly sinusoidal waveform. In other applications, the embodiments shown in FIGS. 29 and 29 may provide better distortion mitigation when the grid load waveform includes a significant amount of distortion.

The principles of the present invention relating to predistortion are not limited to systems with sinusoidal AC rods. The predistortion signal Ma 'may be generated to compensate for distortion in a rod having waveforms such as triangle waves, sawtooth waves, rectangular waves, and the like. In embodiments with a lookup table, the lookup table may be static or may change over time in response to various inputs, such as, for example, line voltage, frequency, link voltage or any other operating parameter. In addition, the distortion mitigation technique in accordance with the principles of the present invention may be realized using any suitable algorithm, including some algorithms from the audio industry, which may be applied directly or in conjunction with the principles of the invention.

The various inventive principles related to distortion mitigation can all be used individually or in combination with other inventive principles. For example, in some embodiments, in accordance with some inventive principles of the present patent disclosure, the controller can combine predistortion with link voltage control, while in other embodiments, the controller can control grid current control, preposition. Direct harmonic distortion rejection can be combined with distortion and link voltage control.

Impedance Conversion

Some additional inventive principles of this patent disclosure relate to techniques for providing impedance conversion, determining a maximum power point or other operating point, and / or manipulating a constant power control loop for other purposes.

Referring to FIG. 30, the PV panel is modeled as voltage source V _INTERNAL and series resistor R _INTERNAL . The positive power control loop causes the PV panel to reference the positive load I _PV at the positive input impedance of Z _IN = V _PV / I _PV . Due to the impedance conversion, the constant power applied to the load I _PV is converted into the constant power delivered to the DC link. Power P is constant and equal to V _PV * I _PV . Since the power is constant and the current induced by the H-bridge varies at twice the line frequency, the link voltage V _DCLINK must also vary at twice the line frequency because the product of current and voltage must be constant. Thus, the current delivered to the DC link changes as follows: P / V _DCLINK = V _PV * I _PV / V _DCLINK .

The power transfer from the PV panel to the converter system is maximized when the series resistance R _INTERNAL of the panel matches the impedance represented by the load I _PV , ie Z _IN = R _INTERNAL = V _PV / I _PV .

In some embodiments, a system that implements positive power control as described above may transform a DC / DC converter or other power stage from a low AC impedance path to a high AC impedance path. This can be better understood with reference to FIG. 31, in which the AC load is shown as a current source 100 from which the pulsating current I _AC is drawn. A conventional DC / DC converter is shown as low impedance pass 102. If either capacitor C ₁ or C _DC is a large value, it forms a low impedance path for the common node, preventing the pulsating current I _AC from returning to the PV panel. However, when capacitor C ₁ or C _DC is removed or reduced in size, the DC / DC converter forms a low impedance AC pass between the load 100 and the PV panel. Thus, the pulsating current I _AC appears at the output of the PV panel as a voltage and / or current variation.

However, realizing a constant power control loop in a DC / DC converter can cause the converter to appear as a pass with high AC impedance. Thus, the pulsating AC current I _AC can be prevented from flowing through the DC / DC converter. As a result, all or most of the AC current must flow through the link capacitor C _DC , which causes a large voltage swing across the C _DC due to the low capacitance of the link capacitor.

Because the impedance conversion nature of positive power control results in control operation rather than components embedded in hardware, it can be changed quickly and / or in a controlled manner. For example, the flow-through impedance of the DC / DC converter can be changed instantaneously by the controller. Such a property can be used to provide some beneficial results.

Operating point sweep ( Operating Point Sweep )

According to some inventive principles of this patent disclosure, one such application relates to determining a maximum power point or other operating point for a power source coupled to a power converter. Referring to FIG. 32, curve 104 shows the voltage-current characteristics (VI curve) of a typical PV panel under certain operating conditions, while curve 106 shows the corresponding power characteristic (power curve) for the same panel under the same conditions. ). The VI curve is zero volts at the value of I _SC , the short-circuit current generated by the panel when the output terminals are shorted together. As the output voltage increases, the VI curve is maintained at a fairly constant level of current until it reaches the knee point, and at the knee point, zero current is drawn to V _OC , the open-circuit output voltage of the panel. Descends quickly.

The power curve is simply 'current times voltage' at each point along the V-I curve. The power curve has a maximum value corresponding to a specific voltage level and a specific current level. This is known as maximum power point or MPP. Most PV power systems try to operate at full power point. However, the maximum power point tends to change with changes in operating conditions such as illumination level, temperature, panel age, and the like. Thus, algorithms have been designed to track MPPs that change over time.

Existing algorithms for maximum power point tracking (MPPT) are generally slow processes that are performed over a relatively long frame compared to the AC line cycle duration. In addition, existing algorithms assume that there is only one MPP in the power curve. However, the power curves for some PV panels and other power sources have multiple local power points. One embodiment is shown in FIG. 33 showing the V-I and power curves for a power source having one or more local MPPs. The conventional MPPT algorithm approaches the local maximum MPP1 from the left side and stops when it is determined to face down as the power curve moves to the right side. In this case, the algorithm incorrectly determines that MMP1 is the maximum power point rather than MMP2, which is the true maximum power point. Existing algorithms can be modified in such a way as to keep searching through the remaining voltage ranges, but with current technology, this is a long process.

In a power conversion system with constant power control, a control technique in accordance with some additional inventive principles of this patent disclosure can be addressed to provide maximum power point tracking or other techniques. As mentioned above, the positive power control loop can prevent the power pulse from returning to the power source. This is shown in FIG. 34 where the power stage 108 is controlled by the positive power control loop 110, which prevents power pulses from the AC rod 112 from reaching the power source 114.

By selectively disabling or modifying the positive power control loop, some or all of the power pulsations can be returned to the power source in a way that can be observed for purposes of determining the operating point or for other useful information. For example, in FIG. 35, control loop 110 is disabled by SW1. This allows the power stage to operate in several different modes, such as a fixed duty cycle, such that current pulsations from the AC load reach the power source. The tracking circuit 116 measures the resulting voltage and / or current variations in the output from the power source 114 and uses that information to perform MMPT algorithms or other processes. The use of relatively small energy storage devices, such as small capacitors, may enable power pulsations from the AC load to reach the power source. For example, if a larger capacitor is used, the pulse may be blocked from returning to the source.

36 shows how the embodiments of FIGS. 34 and 35 work under some conditions. The system is initially assumed to operate at point B where a constant power control loop is available. The control loop is then disabled so that the power stage 108 operates the open loop in a fixed duty cycle. Power pulsations from the AC load return to the power source, causing the operating point to lie between point A and point C when the output voltage and current from the power source sweeps through the corresponding range (V _SWEEP and I _SWEEP ). This causes the driver to ride back and forth along the power curve. The tracking circuit 116 can monitor the output voltage and current to calculate power at all points between A and C. Since the swept range includes both the local maximum points MPP1 and MPP2, the tracking circuit can compare them to determine the true MPP.

In this example, the true MPP is found to be at point B '. Once the MPP is determined, the positive power loop can be made available again to keep the system at B ', regardless of variations in the AC load. In the absence of a positive power control loop, the change in AC load causes the operating point to change around point B ', as shown by the arrows in FIG.

The tracking operation described above is fast in determining MPP or other operating points because, in some cases below the line cycle of the AC rod, the larger operating range can be swept over a smaller time range than typically used in MPPT routines. Can provide a solid technology. For example, in a system with a sinusoidal output, the information in the first phase is the same as the second phase. Thus, in a system with a 60 Hz sinusoidal output, only half a cycle of 120 Hz power ripple is required to get all the information. Thus, sweeping can be performed at 1/4 or ˜4 ms of the 60 Hz line cycle.

The implementation is fast and simple because the positive power control loop can easily be enabled, disabled or changed in the control algorithm. During the sweeping process, perturbation by the AC load may be provided to reduce or eliminate the need for additional circuitry to produce the perturbation.

In addition, the process is very flexible and can be adapted to numerous changes in numerous parameters. For example, the power stage may be set to any suitable fixed duty cycle or other mode of operation during the sweeping operation. Optionally, the duty cycle can be stepped through other values to extend the sweep range over a course of multiple cycles for the AC rod. The system may be configured to sweep the entire operating range of the power source, or fixed or flexible boundaries may be placed in the sweep range. For example, in some embodiments, the sweep operation may be adapted to simply sweep using a particular fixed duty cycle at the power stage by a particular AC load, whatever range is provided. In other embodiments, the limit may be set at the output voltage and / or current from the power source. For example, once a high or low limit is reached, the positive power control loop can be made available at the original operating point B or some modified operating point, such as the limit itself. Thus, if the entire dynamic range does not need to be sampled, the control loop itself can be used to limit the swing through the V-I curve and the power curve.

Sweep operation according to some principles of the invention can be initiated in response to various events. In some embodiments, the sweep operation may be initialized at periodic time intervals, such as once every second or every few seconds, once every minute or every few minutes, and the like. In another embodiment, the sweep operation may be executed if the monitoring operation determines that the system is not operating where it is normally expected to operate. Alternatively, the sweeping operation can be initiated by an external stimulus.

In the example embodiment of FIGS. 34 and 35, although the AC rod itself is used to make a variation in the power source, other devices may also be used to produce a corrected variation. For example, the controllable load can replace a normal AC load to provide a variation within the controlled boundary at a controlled rate. Optionally, the controllable load may provide one or more individual load points, rather than sweeping through all the points within a range. The controllable load can be controlled independently or by the same control circuit used for the tracking task.

Any or all of these features can be realized in a dedicated controller or logic, or in a controller or logic that can realize other features of a power conversion system.

Multiple power sources with individual power control

Some further inventive principles of this patent disclosure relate to the use of power control in systems with multiple power sources. FIG. 37 shows an embodiment of a system in which N multiple power sources 118 are each coupled to a corresponding one of the N power converters 120. The output of the power converter is coupled by the combiner 122 and applied to the at least one energy storage device 124. The outputs of the power converters can be combined in series, parallel, series-parallel combination, or any other suitable arrangement. Power sources include optoelectronic devices, fuel cells, batteries, wind turbines or any other power source or combinations thereof. The power converter may include one or more power sources such as a DC / DC converter, a DC / AC inverter, a rectifier, or any combination thereof. One or more power converters include a constant power control function 126.

38 in accordance with principles of some inventions of this patent disclosure, illustrates an embodiment of a power conversion system in which multiple DC / DC converters include a constant power control function. In the embodiment of FIG. 38, the power source is realized as PV panels 128, where each PV panel provides power to a corresponding DC / DC converter 130. The outputs of the DC / DC converters are arranged in series to generate a DC link voltage V _d that is applied to the link capacitor C _DC . The DC / AC inverter 132 converts the link voltage into the AC voltage V _GRID .

Each of the DC / DC converters 130 implements a constant power control loop 134 to maintain constant power transmission from the PV panels with which they are associated. Each of the DC / DC converters 130 may implement a maximum power point tracking function (MPPT) that acts as a slow outer control loop around a relatively fast internal positive power control loop. Each DC / DC converter outputs a constant power that corresponds to the input power provided by each of the individual power sources. The link capacitor C _DC acts as any combination energy storage element in the DC / DC converter. The link voltage Vd comprises an AC ripple component on top of the DC component, the amount of AC ripple being dependent on the size of the link capacitor, discussed below. The output voltage and current from each DC / DC converter may allow for float to settle to a value that balances the voltage and current constraints of the overall power system. Because converter 130 is arranged in series in this example, the sum of the output voltages must be equal to the DC link voltage V _d , so that the output current through each DC / DC converter can be the same. In other embodiments, it may be arranged for other constraints. For example, in embodiments where the DC / DC converters are connected in parallel, each converter can provide a different amount of current.

In addition, the system of FIG. 38 maintains an average or RMS value of the link voltage at a level that provides optimum operation of the DC / AC inverter, and / or suppresses or reduces harmonic distortion at the output. It may include a link voltage control function to adjust the demand from the inverter.

Since each of the DC / DC converters 130 implements a separate constant power control loop, the input ripple in each converter can be optimally minimized for each PV panel. By adding the MPPT function to each converter, the power output from each PV panel can be optimized regardless of the difference in operating conditions for each panel, eg lighting conditions, temperature, age, etc.

In addition, the size of the link capacitor C _DC can be reduced depending on the implementation details. For example, an embodiment having a DC / AC inverter 132 with harmonic distortion mitigation characteristics may reduce the size of the link capacitor. Although more capacitors are used as a result of large voltage variations on the link capacitors, the presence of harmonic distortion mitigation characteristics can reduce distortion at the AC output to an acceptable level. However, in embodiments with conventional DC / AC inverters without harmonic distortion mitigation, there is still a need to use relatively large link capacitors due to the large ripple voltage on the link capacitors causing unacceptable levels of distortion at the AC output. have.

Some additional inventive principles of this patent disclosure relate to power conversion system structures realized using some or all of the principles of other inventions, including single or various combinations. Some of these structures will be described with reference to the following drawings.

FIG. 39 illustrates an embodiment where multiple modules 400, including some or all of static power control 402, are arranged in series to create a DC link V _LINK that is applied to a conventional central inverter 404. Illustrated. Due to the use of a conventional central inverter 404, a relatively large link capacitor C _LINK is useful for limiting AC ripple and providing a constrained DC link that prevents excessive distortion at the AC output.

40 illustrates an embodiment in which multiple modules 400 are arranged in parallel, including some or all of static power control 402.

41 illustrates a parallel-serial embodiment in which multiple modules 400 are initially arranged in a parallel unit. The parallel units are then arranged in series to provide a DC link V _LINK .

42 illustrates a serial-parallel embodiment, in which multiple modules 400 are first arranged in a serial unit or strings. The individual strings are then arranged in parallel combination to create a DC link V _LINK .

In each embodiment of FIGS. 39-42, a module may be, for example, one or more solar panels, fuel cells, or other power sources, with, in some embodiments, each module 400 having a positive power control 402 integrated into a source. It can be implemented in various optional structures. In another embodiment, the module may include one or more power sources that further associate a DC / DC converter in which the positive power control 402 becomes part of the DC / DC converter. Other modular configurations may include combinations that disclose them.

In addition, in each embodiment of FIGS. 39-42, because a conventional central inverter 404 is used, a relatively large link capacitor C _LINK restricts AC ripple and prevents constrained DC links that prevent excessive distortion at the AC output. Useful to provide.

Some additional inventive principles relate to the use of harmonic distortion mitigation in a central inverter or other power stage combining one or more power sources with constant power control.

43 illustrates an embodiment in which a central inverter is based on an inverter bridge 406 that includes harmonic distortion mitigation 408 in accordance with the principles of the invention of this disclosure. In this embodiment, the DC link V _LINK may be generated by one or more power sources, including some or all of the positive power control. For example, any of the power source arrangements indicated in FIGS. 39-42 can be used to generate V _LINK . However, since the H-bridge 406 includes a high frequency distortion mitigation 408, the ripple limit on the V _LINK can be relaxed, so that a smaller link capacitor can be used. That is, large voltage variations can be tolerated at V _LINK without causing excessive distortion at the AC output due to the operation of harmonic distortion mitigation 408. Thus, one or more power sources with positive power control may be allowed to create a relaxed DC link on a smaller capacitor.

FIG. 44 shows another embodiment of a central inverter capable of operating with a relaxed DC link. In this embodiment, the inverter includes a push-pull stage 410, rectifier 414, and inverter bridge 406 that are followed by transformer 412 to provide isolation. Inverter bridge 406 includes harmonic distortion mitigation 408. In this embodiment, energy storage can be provided by a relatively small DC link capacitor C _LINK arranged between the rectifier and the inverter bridge. In another embodiment, the link capacitor is arranged in front of the push-pull stage as shown in FIG. In yet another embodiment, energy storage can be distributed among multiple locations. In addition, any of these embodiments may include other power stages, such as preregulators and the like. Likewise, MPPT may be included at any suitable point, such as at the input of a push-pull stage or inverter bridge.

46 shows another embodiment of a central inverter capable of operating with a relaxed DC link. In this embodiment, the relaxed DC link input is applied to DC / DC converter 416, which also includes constant power control 418. The output of the DC / DC converter stage is applied to an inverter bridge 406 with distortion mitigation 408. A relatively small DC link capacitor C _LINK is arranged between the DC / DC converter and the inverter bridge.

47 shows another embodiment of a central inverter capable of operating with a relaxed DC link. In this embodiment, the relaxed DC link input V _LINK is applied to the line-frequency inverter bridge 407 with the distortion mitigation 409. The output from the inverter bridge is applied to a line-frequency transformer 441 that couples the inverter to a power grid or AC load.

Some additional inventive principles relate to the use of harmonic distortion mitigation in a stage of constant power control and a stage of a central inverter or other power stage or a combination with one or more conventional power sources.

48 illustrates an embodiment of a central inverter that can operate with direct input from one or more power sources such as PV panels, fuel cells, and the like. One or more power sources create a DC bus V _BUS that inputs to DC / DC converter 420 with constant power control 422. The DC / DC converter is followed by an inverter bridge 406 having a push-pull stage 410, a transformer 412, a rectifier 414 and a distortion mitigation 408.

Due to the positive power loop that prevents ripple on the capacitor from reflecting back to one or more power sources, a relatively small capacitor can be used as the link capacitor C _LINK , while distortion mitigation is at the AC output caused by the ripple on the DC link. Distortion can be suppressed or reduced. Thus, a relaxed DC link can be used.

In the embodiment of FIG. 48, the link capacitor C _LINK is arranged between the rectifier and the inverter bridge, but in another embodiment, the link capacitor is a DC-DC converter 420 and a push-pull stage as shown in FIG. 49. 410 or any suitable location of the inverter.

In the embodiment of Figs. 48, 49, the MPPT function can also be implemented in a DC / DC converter in the inverter bridge, or in other cases in an inverter for setting an operating point for constant power control, whereby a power source Or maximize power transfer from the source on the DC bus.

The principles of the invention described with respect to the embodiments of FIGS. 44-49 can be applied to central inverters, distributed inverters, combinations thereof, and the like.

Some additional principles of the invention relate to the use of distortion mitigation with distributed inverters, referred to as micro inverters or nano inverters.

50 illustrates an embodiment of a system in which multiple distributed inverters 424 receive power directly from multiple power sources 430. Some or all of the inverter includes constant power control 426 and distortion mitigation 428. The outputs from the distributed inverters are combined to provide an AC output to a grid or other AC load.

51 illustrates an embodiment of a system in which multiple distributed inverters 432 receive power from multiple power sources 436. Some or all of the power sources include positive power control 438 that provides a relaxed DC link to the inverter, and some or all of the inverter is caused by distortion that causes ripple on the relaxed DC link that is unacceptable at the AC output. Distortion mitigation 434 that prevents it. The outputs from the distributed inverters are combined to provide an AC output to a grid or other AC load.

In the embodiment of FIGS. 50 and 51, the MPPT function can also be implemented in a distributed inverter or in any power source for setting an operating point for positive power control, thereby allowing power transfer from or to the power source. Maximize.

Applications

Although some inventive principles of this patent disclosure have been described in the context of some specific embodiments related to DC-to-AC inverter systems, the principles of the invention provide for a power conversion system in which the system recognizes dynamic loads and / or dynamic power sources. There is a need for an energy storage device that has a wide range of applications in a wide range of and thus balances the flow of power from source to load. The principles of the invention can be particularly advantageous where reliability is important and where energy storage devices are typically unreliable. Some examples of suitable applications are as follows. Electric and hybrid cars, forklifts, passenger means, trams, metro systems; Air cooling system; Solar and wind energy systems including inverter / converter boxes; Energy storage (battery) decoupling; All kinds of power supplies; All kinds of motor drives; Energy conversion systems such as battery chargers and charge controllers; Induction heating; EMI reduction filters, including high voltage applications.

In addition, the principles of some inventions relate to the constant power control described in the context of embodiments with relatively stable power sources and varying loads, but can also be applied to systems with varying power sources and relatively stable loads as well. have. This may also apply to systems with both varying power and varying load with a relatively stable power link between the source and the load. In general, constant power control may be applied to separate one or more regions with relatively stable power from one or more regions with varying power.

For example, the principles of the invention regarding static power control can be applied to energy conversion: (a) from sun to grid, from fuel cell to grid, such as from DC to AC; (b) from grid to battery, such as from AC to DC; (c) from AC to all kinds of motors, etc. on the production line, such as from AC to variable mechanical load; (d) from batteries to electric motors in electric vehicles (EVs), such as from DC to variable mechanical loads; (e) from a wind turbine to a grid, such as from a variable mechanical generator to an AC load; (f) from a wind turbine to a battery, such as from a variable mechanical generator to a DC load; Etc. In some embodiments, the mechanical rod can be, for example, a heat rod in induction heating.

Examples of other descriptions relating to the application of the principles of the invention relate to static power control in wind turbines that feed grids or other AC loads. If the wind flow is stable, that is, a type of turbulent flow versus laminar flow, the power obtained is uniform. It is inferred to be constantly irradiated on the PV panels. Therefore, uniform power flow should be stored on a cycle-by-cycle basis for transmission to the AC grid. This is inferred as cycle-specific power storage that transfers DC power from the PV panel to the AC load.

On the other hand, if the wind flow is unstable, the power obtained is dynamic, but faster and more variable to infer with a shadowing effect on the PV panel. In this situation, the principles of the present invention relate to combining fast MPPTs with cycle-by-cycle energy storage that can utilize beneficial effects. That is, fast MPPT can be used to determine the best operating point at frequent intervals, while a constant power control loop can be utilized to maintain the system at the most recently determined operating point.

53 illustrates another embodiment of a power converter system in accordance with the principles of the invention of this patent disclosure. Power path 148 transfers power from power source 154 to load 156. The power pass includes an energy storage device 150 and a power stage 152. The controller 158 causes a power stage to control power to or from the energy storage device. The power may be controlled to a constant value, a variable value, and the like. The power from the power source has a constant value, a variable value, and the like. The load power has a constant value, a variable value, and the like.

Some additional inventive principles of this patent disclosure relate to mitigation of electromagnetic interference (EMI).

52 illustrates an embodiment of a power conversion system with EMI mitigation in accordance with the principles of the invention of this patent disclosure. Power path 140 has one or more power stages that transfer power from power source 138 to load 142. Positive power control 144 causes the power path to present a positive input impedance at the power source. EMI mitigating element 146 operates on the power path to reduce or eliminate EMI occurring in the power path.

While the principles of the invention of this patent disclosure have been described above by reference to some specific embodiments, these embodiments may be adjusted in an arrangement or detail without departing from the spirit of the invention. For example, some embodiments have been described in the context of delivering power to an AC grid, but the principles of the invention apply, of course, to other forms of load. In another example, some embodiments describe a capacitor as an energy storage device, and while the DC link voltage is fluctuating, the principles of the invention relate to other forms of energy storage device, for example a DC link having an AC ripple current instead of a voltage. Applied to inductances that can provide current. In another example, any of the constant power control techniques described so far may, of course, be implemented with variable power control, or any other type of power control. Such changes and adjustments are considered to be within the scope of the following claims.

Claims (39)

A converter for transferring power from a power source to a load, the converter having a power stage and an energy storage device;
A converter inducing the power stage to control power to or from the energy storage device
System comprising a. The method of claim 1,
The power is controlled to a substantially constant value. The method of claim 1,
The power is controlled to a variable value. The method of claim 1,
The power source or rod has a substantially constant power. The method of claim 1,
The power source or load has a varying power. A converter for transferring power between the power source and a load having a varying power demand; And
Converter with power control
Including,
The converter comprises a push-pull stage and an energy storage device following the push-pull stage. The method of claim 6,
The power control substantially includes constant power control or variable power control. The method of claim 6,
The controller is arranged to control a parameter of the energy storage device. A power control circuit for providing power control to the power converter; And
A power switch coupled to the power control circuit to operate the power converter
Integrated circuit comprising a. 10. The method of claim 9,
A second power switch coupled to the power control circuit for operating the power converter
Integrated circuit further comprising. The method of claim 10,
The first and second power switches are configured to operate a push-pull stage in the power converter. 10. The method of claim 9,
An integrated circuit further comprising a distortion mitigation circuit. 10. The method of claim 9,
And circuitry for controlling parameters of an energy storage device in the power converter. 10. The method of claim 9,
And circuitry for sweeping operating points at the input of the power converter. 10. The method of claim 9,
An integrated circuit further comprising an EMI mitigation circuit. Two or more power converters that convert power from two or more sources to one or more loads with varying power demands
Including,
Wherein the two or more power converters have power control. The method of claim 16,
The two or more power converters have outputs coupled in series, in parallel, series-parallel, or in parallel series. The method of claim 16,
The two or more power converters have a combined output to provide power with the same load. The method of claim 18,
And an energy storage device coupled to the combined output of the first and second converters. The method of claim 18,
The output from each converter allows for float. A converter for transferring power between the power source and a load having a varying power demand;
A converter providing power control; And
Distortion Mitigation Circuit
System comprising a. The method of claim 21,
The converter comprises an energy storage device,
And the distortion mitigation circuit controls the parameters of the energy storage device. The method of claim 22,
The distortion mitigation circuit tilts the DC region of the parameter to prevent the AC region of the parameter from becoming excessive and causing unacceptable distortion. The method of claim 21,
And the distortion mitigating circuit comprises a sine generator. The method of claim 21,
And the distortion mitigating circuit comprises a predistortion circuit. The method of claim 21,
The controller includes grid current control. A converter for transferring power between the power source and a load having a varying power demand; And
Controller provides power control
Including,
The controller selectively disables the power control. The method of claim 27,
The power control prevents power fluctuations from reaching the power source, and
A system for disabling power control that may vary in power to reach the power source. The method of claim 27,
And a tracking circuit for monitoring the power source. The method of claim 29,
The tracking circuitry determines an operating point when the power control is deactivated. The method of claim 30,
The operating point includes a maximum power point. The method of claim 29,
The power control is deactivated periodically or when an operating parameter of the converter deviates from an expected value. 33. The method of claim 32,
The controller re-enables the power control when an operating parameter of the converter exceeds a limit. A power pass having a first power stage coupled to an input of the power pass; And
A converter that generates a drive signal to provide power control in response to the sensed signal from the power path,
The sense signal is taken from a different location than the input of the power path, and the drive signal is applied to the power path that is different from the first power stage. The method of claim 34, wherein
The sense signal is taken from an output of the power path. The method of claim 34, wherein
The power is controlled by controlling a parameter of the power path to a constant value. The method of claim 34, wherein
The power is controlled by controlling a parameter of the power path to a varying value. The method of claim 34, wherein
The power path is,
An energy storage device that follows the first power stage; And
A second power stage having an input coupled with the energy storage device
System comprising a. The method of claim 38,
The drive signal is applied to the second power stage.

Images