WO2016057395A1

WO2016057395A1 - Circuit and method for a resonant tank

Info

Publication number: WO2016057395A1
Application number: PCT/US2015/054003
Authority: WO
Inventors: Ramanujam Ramabhadran; Giampaolo Carli; Saijun Mao
Original assignee: General Electric Company
Priority date: 2014-10-09
Filing date: 2015-10-05
Publication date: 2016-04-14
Also published as: CN105576977B; CN105576977A

Abstract

A power conversion circuit is provided. The power conversion circuit includes a square wave generator, a resonant tank, a transformer and a controller. The square wave generator is for generating a square wave power. The resonant tank is for receiving the square wave power and outputting a first resonant power. The resonant tank includes a capacitor, an inductor and a controllable capacitive device. The transformer is coupled with the controllable capacitive device for receiving the first resonant power and outputting a second resonant power. A rectified second resonant power is provided to a load. The controller is for generating a switching signal to the controllable capacitive device based on a comparison result between a threshold signal and a signal calculated based on at least one detected signal of the load. A method for controlling a power conversion circuit and a resonant tank are also provided.

Description

CIRCUIT AND METHOD FOR A RESONANT TANK

BACKGROUND

[0001] Embodiments of the invention relate generally to circuits and methods for extending power regulating range of a power conversion circuit, and more particularly to circuits and methods of employing a controllable capacitive device in a resonant circuit of the power conversion circuit.

[0002] Power conversion circuits are widely used in various fields such as

communication, lighting, vehicle, military and etc. for providing suitable power. As a requirement of lo power loss and energy saving, some resonant circuits such as an LC resonant tank, an LLC resonant tank or an LCC resonant tank which help the power conversion circuits operate with a high efficiency and an extended power regulating range are used.

10003] In reference to the light emitting diode (LED), for example, a dimming function utilizes a wide power regulating range. As an LED array can't be driven directly from an AC power source or a fixed DC power source, the power conversion circuii is used to convert an AC power or a DC power into an output DC power. The power conversion circuii should nominally exhibit high electrical conversion efficiency (e.g., 90%) with a high power factor while providing a controllable current to the LED array. When the AC power source is used, a power factor correction (PFC) circuit is further used to generate a DC power. The DC power source or the PFC circuit can output a constant voltage (e.g., 380V~450V), the resonant circuit is easily designed to realize a wide power regulating range.

[0004] The LCC resonant tank is a series-parallel resonant structure which includes an inductor, a capacitor and a shunt capacitor. The LCC resonant tank is commonly used in the power conversion circuit. A variable frequency control is employed in a half bridge having two semiconducting switches coupled in series to realize load power regulation. The LCC resonant tank is connected with a middle point between the two semiconducting switches. A large part of the current which flows from the middle point through the LCC resonant tank- can be shunted by the shunt capacitor.

[0005] However, a fixed LCC resonant tank is not suitable for all kinds of LED array. Under some circumstances, the frequency of the switching signal is too high which causes high switching losses when dimming the LED array. Under some circumstances, the power regulating range is too narrow although the frequency of the switching signal is within a wide range.

[Θ0Θ6] Therefore, there is a need for providing a new circuit or method to solve at least one of the above problems.

BRIEF DESCRIPTION

[00Θ7] In accordance with an embodiment of the invention, a power conversion circuit is provided. The power conversion circuit includes a square wave generator, a resonant tank, a transformer and a controller. The square wave generator is for generating a square wave power. The resonant tank is for receiving the square wave power and outputting a first resonant power. The resonant tank includes a capacitor, an inductor and a controllable capacitive device. The capacitor and the inductor are coupled in series between the square wave generator and the controllable capacitive device. The transformer is coupled with the controllable capacitive device for receiving the first resonant power and outputting a second resonant power. A. rectified second resonant power is provided to a load. The controller is for generating a switching signal to the controllable capacitive device based on a comparison result between a threshold signal and a signal calculated based on at least one detected signal of the load.

[00Θ8] In accordance with another embodiment of the invention, a method for controlling a power conversion circuit is provided. The method includes receiving at leasi one detected signal of a load. The method includes calculating a signal based on the at least one detected signal. The method includes comparing the signal with a threshold signal. The method includes generating a switching signal to a controllable capacitive device of the power conversion circuit based on a comparison result of the signal and the threshold signal.

[00Θ9] In accordance with another embodiment of the invention, a resonant tank is provided. The resonant tank includes a first branch and a second branch. The first branch includes a capacitor and an inductor coupled in series. The second branch is coupled with the first branch. The second branch includes a controllable capacitive device for shunting a part of current flowing through the first branch. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

[0011] FIG. I is a schematic diagram of a power conversion circuit in accordance with one exemplary embodiment;

[0012] FIG. 2. is a schematic diagram of a power conversion circuit in accordance with another exemplary embodiment;

[0013] FIG, 3 is a schematic diagram of a power conversion circuit in accordance with another exemplary embodiment;

[0014] FIG. 4 is a schematic diagram of a power conversion circuit in accordance with another exemplary embodiment;

[0015] FIG. 5 is a waveform view of a current with variable frequency and variable capacitor in accordance with one exemplary embodiment;

[0016] FIG . 6 is a waveform view of a current with variable frequency and variable capaciior in accordance with another exemplary embodiment; and

[0017] FIG. 7 is a flowchart of a method for operating a power conversion circuit in accordance with one exemplary embodiment.

DETAILED DESCRIPTION

[0018] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this invention belongs. The terms "first", "second", and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms "a" and "an" do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items, unless otherwise noted, are merely used for convenience of description, and are not limited to any one position or spatial orientation.

[001 ] Referring to FIG. 1 , a schematic view of a power conversion circuit 10 in accordance with one exemplary embodiment is shown. The power conversion circuit 1 0 includes a square wave generator 103, a resonant tank 105, a transformer 107, a rectifier 109 and a controller 150.

[0028] The square wave generator 103 is configured to receive a DC power generated from a DC input source 101 via a high voltage terminal 102 and a low voltage terminal 104 and output a square wave power. In some embodiments, the DC power is generated from a power factor correction (PFC) circuit when the input source 101 is an AC power source.

[0021] As shown in FIG. 1, the square wave generator 103 includes a half bridge circuit which includes a first switch 11 1 and a second switch 1 13 coupled in series. The first switch 1 1 1 is coupled to the high voltage terminal 102 of the DC input source 101. The second switch i 13 is coupled to the low voltage terminal 104 of the DC input source 101. The input DC power is converted into a square wave power at a middle point O between the first switch 1 1 1 and the second switch 1 13.

[0022] The first switch 11 1 and the second switch 1 13 may include any types of semiconducting switches such as Metal-Oxide Semiconductor Field Effect Transistor (MOSFET), Insulated Gate Bipolar Transistor (IGBT) and etc. In this embodiment, the half bridge 103 further includes an upper anti-parallel diode 1 15 coupled with the first switch 111 and a lower anti-parallel diode 117 coupled with the second switch 1 13. In some embodiments, the square wave generator 103 may include other types of circuit like an H- bridge.

[0023] The resonant tank 105 is configured to receive the square wave power and output a first resonant power. The resonant tank 105 includes a first branch and a second branch coupled with each other. The first branch is coupled between the square wave generator 103 and the second branch, more specifically, between the middle point O of the half bridge 103 and a point A. The first branch includes a capacitor 121 and an inductor 23 coupled in series. The second branch includes a controllable capacitive device 124 for shunting a part of current flowing through the first branch. In this embodiment, the resonant tank 105 is called a LCC resonant tank.

[0024] m the illustrated embodiment of FIG. 1 , the controllable capacitive device 124 includes a first capacitor 125, a second capacitor 127 and a switch 129. The second capacitor 127 is coupled with the first capacitor 125 in parallel and the switch 129 is coupled with the second capacitor 127 in series. When the switch 129 is tamed off, the second capacitor 127 is cut off from the first capacitor 125. When the switch 129 is turned on, the second capacitor 127 is coupled with the first capacitor 125, Therefore, the capacitance of the controllable capacitive device 124 is variable when operating the power conversion circuit 10.

[0025] In another embodiment as shown in FIG. 2, the controllable capacitive device 224 includes a first capacitor 225, a second capacitor 22.7 and a switch 229. The second capacitor 227 is coupled with the first capacitor 225 in series and the switch 229 is coupled with the second capacitor 227 in parallel. When the switch 229 is turned on, the second capacitor 227 is short circuited. When the switch 229 is turned off, the second capacitor 227 is coupled with the first capacitor 2.2.5. Therefore, the capacitance of the controllable capacitive device 224 is variable when operating the power conversion circuit 20. In other embodiments, the controllable capacitive device may include more than two capacitors coupled in parallel or in series.

[0026] In another embodiment as shown in FIG. 3, compared with the embodiment of FIG. 1, the resonant tank 105 further includes a clipping circuit 147 formed by two diodes 148 and 149. The clipping circuit 147 is coupled with the controllable capacitive device 124 and the square wave generator 103. A cathode of the diode 149 is coupled to the high voltage terminal 102. of the DC input source 101 and an anode of the diode 149 is coupled io the point A. A cathode of the diode 148 is coupled to the point A and an anode of the diode 148 is coupled to the low voltage terminal 104. The clipping circuit 147 constrains an AC voltage of the controllable capacitive device 124 within a DC voltage of the DC input source 101. The clipping circuit 147 can prevent high resonant voltage from damaging the components in the resonant tank 105. Similarly, in another embodiment as shown in FIG. 4, compared with the embodiment of FIG. 2, the clipping circuit 147 is further included and the clipping circuit 147 is illustrated above so the detailed description is omitted here.

[0027] Referring back to FIG. 1 , the transformer 107 includes a primary winding 135 and a secondary winding 137. An inductor 131 and a capacitor 133 are coupled in series and then coupled with the controllable capacitive device 124 in parallel. The primary winding 135 is coupled with the inductor 131 in parallel. A fter the shunting of the controllable capacitive device 124, the other part of current flows through the primary winding 135 as the first resonant power. The secondary winding 137 is electromagnetieally coupled with the primary winding 135 and a second resonant power is induced in the secondary winding 137.

[0028] The rectifier 109 is coupled with the secondary winding 137. The rectifier 109 is configured to receive the second resonant power and output a rectified second resonant power for providing to a load 143. The load 143 includes a LED array or any other types of DC load. Take the LED array 143 for example, a wide power regulating range and low loss are necessary for the LED array 143 to realize the dimming function. In some embodiments, a variable frequency control of the switching signals provided to the first switch 1 11 and the second switch 113 is implemented in the controller 1 0.

[0029] In some embodiments, a current close-loop control algorithm is employed in the controller 150 since the LED array 143 is a current control element. When the current flows through the LED array 143 changes, the power of the LED array 143 is regulated in a wide range. And variable frequency switching signals 175 and 173 are generated to drivers 165 and 163 for driving the first switch 1 11 and the second switch 1 13 respectively. The variable frequency control manner is commonly used in this power conversion circuit 10 for adjusting a feedback load current signal to track a current reference signal.

[0038] In this embodiment, some sensors such as a current sensor and/or a voltage sensor (not shown) can be used to def ect a current, a voltage and/or a power of the LED array 143 and generate at least one detected signal 153. The controller 150 receives the at least one detected signal 153 and calculates a signal 155 based on the at least one detected signal 153. For example, a power ratio 155 can be calculated based on a ratio of an actual power and a rated power. The actual power can be calculated based on the detected current and voltage signals 153. The controller 150 is configured to compare the signal 155 with a threshold signal 151 and generate a switching signal 171 to the controllable capacitive device 124 based on a comparison result between the signal 155 of the load 143 and the threshold signal 151.

10031] For the embodiment of FIG. 1, when the signal 155 is a power ratio, the threshold signal 151 is a threshold power ratio. For example, 30% can be set as the threshold power ratio which represents a light load. The switch 129 is turned on or turned off based on the comparison result between the threshold signal 151 and the signal 155. [0032] When the LED array 143 is operated in a heavy load status, more specifically, when the signal 155 is beyond the threshold signal 151, the controller 150 is configured to generate a first switching signal (e.g., OFF signal) as the switching signal 171 for providing to a driver 161 of the switch 129. Then the switch 129 is driven to be turned off and the second capacitor 127 is cut off. Under this circumstance, the capacitance of the controllable capacitive device 124 is low,

[0033] Otherwise, when the LED array 143 is operated in a light load status, more specifically, when the signal 155 is not beyond the threshold signal 151, the controller 150 is configured to generate a second switching signal (e.g., ON signal) as the switching signal 171 for providing to the driver 161 of the switch 129. Then the switch 129 is driven to be turned on and the second capacitor 127 works together with the first capacitor 125. Under this circumsiaiice, the capaciiaiice of the controllable capacitive device 124 is increased.

[0034] Similarly, for the embodiment of FIG. 2, when the LED array 143 is operated in a heavy load status, more specifically, when the signal 155 is bey ond the threshold signal 151 , the controiler 150 is configured to generate a first switching signal (e.g., OFF signal) as the switching signal 171 for providing to a driver 161 of the switch 229. Then the switch 229 is driven to be turned off and the second capacitor 227 works together with the first capacitor 225. Under this circumstance, the capacitance of the controllable capacitive device 224 is low.

[0035] Otherwise, when the LED array 143 is operated in a light load status, more specifically, when the signal 155 is not beyond the threshold signal 151 , the controller 150 is configured to generate a second switching signal (e.g., ON signal) as the switching signal 171 for providing to a driver 161 of the switch 229. Then the switch 229 is driven to be turned on and the second capacitor 227 is short circuited. Under this circumstance, the capacitance of the controllable capacitive device 224 is increased,

[0036] The capaci tance of the controllable capacitive device 124 or 224 influences the frequency of the sw itching signals 173 and 175 and the current of the LED array 143 is illustrated with reference to F G. 1, FIG. 5 and FIG. 6.

[0037] Referring to FIG. 5, a waveform view of a current of the LED array 143 with variable frequency and variable capacitor in accordance with one exemplary embodiment is shown. The horizontal axis refers to as the capacitance of the controllable capacitive device 124 and the vertical axis refers to as the current of the LED array 143. It can be seen that the current caused by the controllable capacitive device 12.4 at different frequencies is nonmonotonic.

[0038] For example, when a reference current signal L-_ef 75 inA is given and an OFF signal 171 is generated, the power conversion circuit 10 is operated at an operation point P and the frequency of the switching signals 173 and 175 is 300 kHz. Then the signal 155 is determined to be not beyond the threshold signal 151, an ON signal 171 is generated and the controllable capacitive device 124 is controlled with a higher capacitance which is illustrated above. The power conversion circuit 10 is operated at an operation point Q and the frequency of the switching signals 173 and 175 is 200 kHz. By designing suitable first capacitor 125 and second capacitor 127 and with the increase of the capacitance of the controllable capacitive device 124, the operation point of the power conversion circuit 10 is regulated from P to Q. It is advantageous at reducing the switching losses and the operating range of frequencies when the frequency of the switching signals 173 and 175 reduces. Therefore, a wide power regulating range and low losses are realized.

[0039] Referring to FIG. 6, a waveform view of a current of the LED array 143 with variable frequency and variable capacitor in accordance with another exemplary embodiment is shown. The horizontal axis refers to as the capacitance of the controllable capacitive device 124 and the vertical axis refers to as the current of the LED array 143. It can be seen that the current caused by the controllable capacitive device 124 at different frequencies is non-monotonic.

[0048] When the frequency of the switching signals 173 and 175 is 150 kHz, with the increase of the capacitance of the controllable capacitive device 124, the operation point of the power conversion circuit 10 can move from M to N when the frequency is kept constant. It is advantageous at realizing lower dimming current for a given frequency. The current of the LED array 143 is regulated within a wide range when the frequency is regulated within a narrow range. Therefore, a wide power regulating range can be realized.

[0041] Referring to FIG. 7, a flowchart of a method 500 for operating the power conversion circuit in accordance with one exemplary embodiment is shown. The method includes the following steps. At block 501 , at least one detected signal of a load is received. At block 503, a signal based on the at least one detected signal is calculated. At block 505, the signal is compared with a threshold signal. At block 507, a switching signal provided to a controllable capacitive device 124 of the power conversion circuit 10 is generated based on a comparison result of the signal and the threshold signal,

[0042] The details of how to operate the power conversion circuit 10 which employs the resonant tank 105 has been illustrated in above embodiments. Therefore, the detailed description is omitted here,

[0043] It is to be understood that a skilled artisan will recognize the interchangeability of various features from different embodiments and that the various features described, as well as other known equivalents for each feature, may be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this disclosure. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

[0044] Further, as will be understood by those familiar with the art, the present invention may be embodied in other specific forms without depending from the spirit or essential characteristics thereof. Accordingly, the disclosures and descriptions herein are intended to be illustrative, but not limiting, of the scope of the invention which is set forth in the following claims.

Claims

CLAIMS:

1. A. power conversion circuit, comprising:

a square wave generator for generating a square wave power; a resonant tank for receiving the square wave power and outputting a first resonant power, wherein the resonant tank comprises a capacitor, an inductor and a controllable capacitive device, the capacitor and the inductor are coupled in series between the square wave generator and the controllable capacitive device;

a transformer coupled with the controllable capacitive device for receiving the first resonant power and outputting a second resonant power, wherein a rectified second resonant power is provided to a load; and

a controller for generating a switching signal to the controllable capacitive device based on a comparison result between a ihreshold signal and a signal calculated based on at least one detected signal of the load,

2. The power conversion circuit of claim 1 , wherein the resonant tank comprises a clipping circuit coupled with the controllable capacitive device and the square wave generator for constraining an AC voltage at the controllable capacitive device.

3. The power conversion circuit of claim 1 , wherein the controllable capacitive device comprises a first capacitor, a second capacitor and a switch, the second capacitor is coupled with the first capacitor in parallel and the switch is coupled with the second capacitor in series,

4. The power conversion circuit of claim 3, wherein the switch is turned on or turned off based on the comparison result between the ihreshold signal and the signal.

5. The power conversion circuit of claim 4, wherein

the switch is tuned on when the signal is not beyond the threshold signal; and the switch is tuned off when the signal is beyond the threshold signal.

6. The power conversion circuit of claim 1 , wherein the controllable capacitive device comprises a first capacitor, a second capacitor and a switch, the second capacitor is coupled with the first capacitor in series and the switch is coupled with the second capacitor in parallel.

7. The power conversion circuit of claim 6, wherein the switch is turned on or turned off based on the comparison result between the threshold signal and the signal.

8. The power conversion circuit of claim 7, wherein

9. The power conversion circuit of claim 1 , wherein the detected signal of the load comprises a current, a voltage or a power of the load.

10. The power conversion circuit of claim 1, wherein the square wave generator comprises a first switch and a second switch, the resonant tank is coupled with a middle point of the first switch and the second switch.

1 1. The power conversion circuit of claim 10, wherein the controller is for generating switching signals to the first switch and the second switch for adjusting a feedback load current signal to track a current reference signal.

12. A method for controlling a power conversion circuit, comprising:

receiving at least one detected signal of a load;

calculating a signal based on the at least one detected signal;

comparing the signal with a threshold signal; and

generating a switching signal to a controllable capacitive device of the power conversion circuit based on a comparison result of the signal and the threshold signal.

13. The method of claim 12, wherein the detected signal of the load comprises a current, a voltage or a power of the load.

14. The method of claim 12, comprising turning on or turning off a switch of the controllable capacitive based on the comparison result between the threshold signal and the signal.

15. The method of claim 14, comprising: turning on the switch when the signal is not beyond the threshold signal; and turning off the switch when the signal is beyond the threshold signal.

16. The method of claim 12, comprising generating switching signals to a first switch and a second switch of a square wave generator for adjusting a load current feedback signal to track a current reference signal.

17. A resonant tank comprising:

a first branch comprising a capacitor and an inductor coupled in series; and a second branch coupled with the first branch, ihe second branch comprising a controllable capacitive device for shunting a part of current flowing through the first branch.

18. The resonant tank of claim 17, wherein a switch of the controllable capacitive device is turned on or turned off based on the comparison result between the threshold signal and the signal.

19. The resonant tank of claim 17, wherein the controllable capacitive device comprises a first capacitor, a second capacitor and a switch, the second capacitor is coupled with the first capacitor in parallel and the switch is coupled with the second capacitor in series.

20. The resonant tank of claim 17, wherein the controllable capacitive device comprises a first capacitor, a second capacitor and a switch, the second capacitor is coupled with the first capacitor in series and the switch is coupled with the second capacitor in parallel.