# Patent

## Title
Energy voltage regulator and control method applicable thereto

## Abstract

A control method for an energy voltage regulator includes: detecting an output AC signal of a current cycle to generate a reference current command; comparing the reference current command with a reference upper power limit; and if the reference current command is lower than the reference upper power limit, generating a first current command based on the reference current command, to perform a discontinuous conduct control and to operate the energy voltage regulator under a discontinuous conduct state.

## Background
CROSS-REFERENCE OF RELATED APPLICATION
This application claims the benefit of Taiwan application Serial No. 103112475, filed Apr. 3, 2014, the subject matter of which is incorporated herein by reference.
TECHNICAL FIELD
The disclosure relates in general to an energy voltage regulator and a control method applicable thereto.
BACKGROUND
Human civilization is established on adequate supply of energy. Once energy supply turns inadequate, the lifestyle and development of modern society will be severely affected. However, the storage capacities of energy sources such as petroleum and natural gas are limited, and energy shortage may trigger energy crisis. Therefore, more and more people are engaged in the development of clean energy with an aim to resolving or mitigating energy crisis. Solar energy is one of the clean energies.
During the generation of solar power, the solar panel converts solar energy into a DC power. After DC-to-DC conversion and DC-to-AC conversion is performed on the DC power outputted by the solar panel, a filter is used to filter high frequency signals off to obtain an AC power. The AC power may then be used by clients or sold to electricity suppliers.
The generation of solar power is closely related to the intensity of sunshine but the intensity of sunshine keeps changing all the time. However, during the operation of solar energy conversion system, operations of the control circuit and switch of the switching element are power consuming. Therefore, how to reduce the power consumption of the solar power regulator is very critical.
SUMMARY
The disclosure is directed to an energy voltage regulator and a control method applicable thereto capable of performing discontinuous conduction control to maintain high-efficiency performance even when the energy voltage regulator is in light-loading and to remove harmonic components off the AC current.
According to one embodiment of the present disclosure, a control method for an energy voltage regulator is disclosed. The method includes: detecting an AC output signal within a current cycle to generate a reference current command; comparing the reference current command with a reference upper power limit; generating a first current command according to the reference current command to perform discontinuous conduction control and to operate the energy voltage regulator under a discontinuous conduction state if the reference current command is lower than the reference upper power limit
According to another embodiment of the present disclosure, an energy voltage regulator comprising a switch circuit, a switch controller, a current command generator, and discontinuous conduction controller is disclosed. The switch controller is coupled to the switch circuit for controlling the switch circuit. The current command generator is coupled to the switch controller for detecting an AC output signal within a current cycle to generate a reference current command and comparing the reference current command with a reference upper power limit. The discontinuous conduction controller is coupled to the switch controller and the current command generator. If the current command generator determines that the reference current command is lower than the reference upper power limit, then the current command generator informs the discontinuous conduction controller to generate a first current command to the switch controller according to the reference current command. The switch controller controls the switch circuit to perform discontinuous conduction control and thus the energy voltage regulator is operated under a discontinuous conduction state.
The above and other aspects of the disclosure will become better understood with regard to the following detailed description of the preferred but non-limiting embodiment (s). The following description is made with reference to the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit diagram of a solar power regulator according to an embodiment of the disclosure.
FIG. 2 is a flowchart of a control method for a solar power regulator according to an embodiment of the disclosure.
FIG. 3 is a signal waveform diagram of a solar power regulator according to an embodiment of the disclosure.



In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.
DETAILED DESCRIPTION OF THE DISCLOSURE
Each of the disclosed embodiments has one or more technical features. In possible implementation, one skilled person in the art would selectively implement part or all technical features of any embodiment of the disclosure or selectively combine part or all technical features of the embodiments of the disclosure.
Referring to FIG. 1, a circuit diagram of a solar power regulator according to an embodiment of the disclosure is shown. As indicated in FIG. 1, the solar power regulator 100 includes a capacitor C1, a pulse width modulation (PWM) switch circuit 110, a controller 120, a current transformer 130 and a filter 140. The PWM switch circuit 110 includes a plurality of switches. In the present embodiment, the PWM switch circuit 110 includes switches SW1 ̃SW4 for description purpose, but the disclosure is not limited thereto.
The controller 120 includes a PWM signal controller 122, a current command generator 124 and a discontinuous current shape controller 126.
FIG. 2 is a flowchart of a control method for the solar power regulator according to the embodiment of the disclosure. FIG. 3 is a signal waveform diagram of the solar power regulator according to the embodiment of the disclosure. Refer to FIG. 1 ̃FIG. 3.
The DC power VDC_IN outputted from the solar panel (also referred as the DC power source) may be stored in the capacitor C1. The capacitor C1 is coupled to the PWM switch circuit 110. The PWM switch circuit 110 is controlled by the PWM signal controller 122 of the controller 120, to convert the DC power stored in the capacitor C1 into AC power.
The PWM signal controller 122 receives a current command Icmd generated by the current command generator 124 and a discontinuous current command Icmd′ generated by the discontinuous current shape controller 126. Basically, at any time, the PWM signal controller 122 receives one of the current command Icmd generated by the current command generator 124 and the discontinuous current command Icmd′ generated by the discontinuous current shape controller 126. That is, the PWM signal controller 122 does not receive both of the current command Icmd generated by the current command generator 124 and the discontinuous current command Icmd′ generated by the discontinuous current shape controller 126 at the same time.
According to the feedback current signal Iac and the received current command (Icmd or Icmd′), the PWM signal controller 122 generates a PWM switch signal to the PWM switch circuit 110 to control switching of the switches SW1 ̃SW4 of the PWM switch circuit 110 to generate an AC output. The AC output generated by the PWM switch circuit 110 is filtered by the filter 140 into an AC voltage Vgrid and an AC current Igrid. The AC voltage Vgrid and the AC current Igrid may be used by clients (such as households or office buildings) or sold to electricity suppliers.
As indicated in step 210 of FIG. 2, a reference current command Iref is generated according to the AC voltage Vgrid and the AC current Igrid. That is, the current command generator 124 generates the reference current command Iref according to the current signal Iac and the voltage signal Vac, wherein, there is a relationship between the current signal Iac and the AC current Igrid. For example, the current signal Iac is obtained by reducing the AC current Igrid, and the voltage signal Vac is obtained by reducing the AC current Vgrid.
If the large-amplitude AC current from the PWM switch circuit 110 is directly inputted to the current command generator 124, the AC current may damage the current command generator 124. In an embodiment of the present disclosure, the current transformer 130 reduces the large-amplitude AC current from the PWM switch circuit 110 as the current signal Iac, which is then inputted to the current command generator 124.
That is, in step 210, after the current command generator 124 detects the current signal Iac and the voltage signal Vac of the current cycle, the current command generator 124 compares the AC voltage Vgrid and the AC current Igrid of a previous cycle with the AC voltage Vgrid and the AC current Igrid of the current cycle by an algorithm (such as the maximum power point tracker (MPPT) algorithm) to generate the reference current command Iref. In some possible embodiments, the reference current command Iref may represent a percentage of the AC current Igrid. Or, in some possible implementations, the reference current command Iref may represent “percentage”.
In step 220, after the reference current command Iref is generated, the current command generator 124 compares the reference current command Iref with the reference upper power limit. For example, the current command generator 124 compares whether the reference current command Iref is higher than a half of the (full-load) AC current. That is, in the case, the reference upper power limit is a half of the full-load AC current. If the judgment in step 220 is positive, then the method proceeds to step 230; and if the judgment in step 220 is negative, then the method proceeds to step 240.
In step 230, the current command generator 124 generates the current command Icmd=Iref to the PWM signal controller 122.
In step 240, the discontinuous current shape controller 126 performs discontinuous conduction control according to the reference current command Iref to generate the discontinuous current command Icmd′ (αi, βi, n) to the PWM signal controller 122.
If the current command generator 124 determines that the reference current command Iref is higher than a half of the full-load AC current Igrid, (i.e. yes in step 220, which implies that the current power output is sufficient and thus the discontinuous conduction control is not needed), the current command generator 124 generates the current command Icmd=Iref to the PWM signal controller 122. If the current command generator 124 determines that the reference current command Iref is not higher than a half of the full-load AC current Igrid, (i.e. no in step 220, which implies that the current power output is not sufficient, and thus the discontinuous conduction control is needed), the current command generator 124 informs the discontinuous current shape controller 126 to perform discontinuous conduction control according to the reference current command Iref to generate the discontinuous current command Icmd′ (αi, βi, n) to the PWM signal controller 122. Moreover, in the same cycle, only one of the current command generator 124 and the discontinuous current shape controller 126 is allowed to generate the current command to the PWM signal controller 122.
In step 250, the PWM signal controller 122 compares the received current command (Icmd or Icmd′) with the feedback current Iac to generate a PWM switch signal to control the switching of the switches SW1 ̃SW4 of the PWM switch circuit 110. The generation of the PWM switch signal by the PWM signal controller 122 is not specified. In an embodiment of the disclosure, if the PWM signal controller 122 receives the current command Icmd=Iref, the PWM switch is under a continuous conduction state. Conversely, if the PWM signal controller receives the current command Icmd′, the PWM switch is under a discontinuous conduction state.
Details of the discontinuous conduction control in the embodiment of the present disclosure are disclosed below.
In the embodiment of the disclosure, the command generator 124 detects the current output current Iac and the current output voltage Vac of the PWM switch circuit to determine the current power output of the solar power regulator 100. The current command generator 124 compares the current power output with the reference upper power limit to determine whether the solar power regulator 100 needs to perform discontinuous conduction control.
If the current power output is lower than the reference upper power limit, then discontinuous conduction control is performed. Under the discontinuous conduction control, the discontinuous current shape controller 126 informs the PWM signal controller 122 to control a pulse width value (during which PWM switches is conducted), such that the solar power regulator outputs the output current Igrid synchronizing with the AC voltage Vgrid.
As indicated in FIG. 3, the discontinuous current shape controller 126 outputs parameters αi, βi and n (i and n are positive integers, 1≦i≦n), wherein, the parameter “αi” represents a width of an action period of the PWM switch circuit, parameter “βi” represents a width of a non-action period of the PWM switch circuit, and the parameter “n” represents a number of conduction times within a half cycle of the AC output voltage (or, number of action periods within a half cycle). As indicated in FIG. 3, n=5.
That is, during the action period αi, the PWM signal controller 122 controls the switching of the switches SW1 ̃SW4 of the PWM switch circuit 110. Conversely, during the non-action period βi, the PWM signal controller 122 completely turns off the switches SW1 ̃SW4 of the PWM switch circuit 110. Besides, both the parameters αi and βi are smaller than a half cycle of the AC output voltage Vgrid, wherein 0≦αi≦180°; and 0≦βi≦180°.
That is, the action period αi is an action period of the solar power regulator, and the non-action period βi is a non-action period of the solar power regulator. That is, during the non-action period βi, the solar power regulator 100 stores the DC power VDC_IN outputted from the solar panel in the capacitor C1. During the action period αi, the solar power regulator 100 converts the electric energy temporarily stored in the capacitor C1 into the AC output voltage Vgrid and the AC output current Igrid.
A power output almost equivalent to the default power output may be obtained by adjusting the number of conduction times n, the action period αi and the non-action period βi.
Also, during each action period αi, the switches are switched at least once (that is, each action period αi includes at least one switching pulse), so that the switches SW1 ̃SW4 convert the DC power VDC_IN outputted from the solar panel into the AC power output. The AC power output has a current waveform of discontinuous conduction type. The output voltage and the output current from the PWM switch circuit 110 are in the same phase and synchronous with the AC voltage Vgrid and the AC current Igrid.
Details of the adjustments of the action period αi, the non-action period βi and the number of conduction times n are disclosed below.
The number of conduction times n is adjusted such that within a half cycle, the summation of the power output of the solar power regulator during the action periods α1 ̃αn is equivalent to the default power output. Suppose the default power output is 10 W. The discontinuous current shape controller 126 outputs the three action periods α1, α2 and α3 and the summation of power output of the solar power regulator during the three action periods α1, α2 and α3 is equivalent to 10 W. That is, if necessary, the number of conduction times n may be increased, such that the solar power regulator may output higher power during more action periods within a half cycle.
Or, the time width of the action period αi is adjusted such that the solar power regulator may generate the default power output within a half cycle. For example, if the default power output is increased by four times, then the width of the action period αi must also be increased by four times such that the power output is increased to match the default power output.
Or, the duty cycle and/or the switching frequency of the switches SW1 ̃SW4 during the action period αi is adjusted, such that the power output of the solar power regulator matches the default power output. For example, if the default power output is increased, then the duty cycle and/or the switching frequency of the switches SW1 ̃SW4 may be correspondingly increased during the action period αi.
If the current power output is over the reference upper power limit, then the solar power regulator does not have to perform discontinuous conduction control. In other words, under such circumstance, the PWM signal controller 122 controls the switches SW1 ̃SW4 of the PWM switch circuit 110 to output currents and voltages to the rear end.
In the embodiment of the disclosure, under a discontinuous conduction state, when outputting the parameters αi, βi and n, the discontinuous current shape controller 126 may adjust the parameters according to the default power output so as to optimize the conversion efficiency and power output quality of the solar power regulator.
In another embodiment of the disclosure, in order to optimize the conversion efficiency, the longest action period αi may correspond to the peak of the power output Vgrid. As indicated in FIG. 3, the action period α3, being the longest action period of the action periods α1 ̃α5 covers the peak of the power output Vgrid, and remaining parameters αi and βi may be symmetrically or asymmetrically arranged at two sides of the longest action period α3. To increase the conversion efficiency, no action period is at the zero-crossing point of the output voltage Vgrid. As indicated in FIG. 3, in order to increase the conversion efficiency, the action period α5, which originally covers the zero-crossing point of the output voltage Vgrid, is cancelled.
In the embodiment of the disclosure, under the circumstance that the power output of the solar panel does not reach the reference upper power limit (that is, the power output of the solar panel is not satisfactory), the solar power regulator operates under a discontinuous conduction control mode. Thus, the solar power regulator is not in action over the entire cycle, and the conduction periods and conduction times of the switches of the PWM switch circuit are adjusted through the adjustment in the parameters αi, βi and n. Within a duty cycle of the AC power output, the number of switching times of the switches of the PWM switch circuit of the embodiment of the present disclosure is lesser than that of the generally known technology, such that switching losses are effectively reduced and the conversion efficiency may thus be significantly increased.
In an embodiment of the disclosure, to reduce the impact caused by the harmonic waves of the discontinuous conduction mode, through the adjustment in the parameter αi, harmonic components of the output current are eliminated to increase the power factor of the output current, such that the solar power regulator 100 will operate under better optimization conditions to achieve higher quality of power output.
Although the above embodiments are exemplified by a solar panel, the present disclosure is not limited thereto. Other embodiments of the present disclosure may also be used in an energy conversion device such as a wind power unit.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.

## Claims

1. A control method for an energy voltage regulator, comprising:
detecting an AC output signal within a current cycle to generate a reference current command signal;
comparing the reference current command signal with a reference upper current signal; and
generating a first current command signal according to the reference current command signal to perform discontinuous conduction control and to operate the energy voltage regulator under a discontinuous conduction state if the reference current command signal is lower than the reference upper current signal;
wherein a width of an action period, a number of the action periods within a half cycle and a width of a non-action period of the energy voltage regulator are determined based on comparison of the reference current command signal and the reference upper current signal;
a second current command signal is generated according to the reference current command signal to perform continuous conduction control and to operate the energy voltage regulator under a continuous conduction state if the reference current command signal is higher than the reference upper current signal;
the second current command signal includes an action period parameter, a non-action period parameter and a number of conduction times parameter;
the action period parameter represents the width of the action period of a plurality of internal switches of the energy voltage regulator;
the non-action period parameter represents the width of the non-action period of the internal switches of the energy voltage regulator; and
the number of conduction times parameter represents a number of conduction times within a half cycle of the AC output signal.

2. The control method according to claim 1, further comprising:
comparing the first or the second current command signal with a feedback current signal to obtain a switching signal, which controls switching of the plurality of internal switches of the energy voltage regulator;
wherein, the feedback current signal is related to the AC output signal detected within the current cycle.

3. The control method according to claim 1, further comprising:
detecting a converted AC output current and a converted AC output voltage within the current cycle to generate the reference current command signal.

4. The control method according to claim 1, wherein:
the reference upper current signal is related to a full-load AC output current.

5. The control method according to claim 1, wherein:
the internal switches are switched at least once within the width of the action period; and
the internal switches are not switched at all within the width of the non-action period.

6. An energy voltage regulator, comprising:
a switch circuit;
a switch controller coupled to the switch circuit for controlling the switch circuit;
a current command generator coupled to the switch controller for detecting an AC output signal within a current cycle to generate a reference current command signal and comparing the reference current command with a reference upper current signal; and
a discontinuous conduction controller coupled to the switch controller and the current command generator;
wherein
if the current command generator determines that the reference current command signal is lower than the reference upper current signal, then the current command generator informs the discontinuous conduction controller to generate a first current command signal to the switch controller according to the reference current command signal, the switch controller controls the switch circuit to perform discontinuous conduction control and thus the energy voltage regulator is operated under a discontinuous conduction state;
wherein a width of an action period, a number of the action periods within a half cycle and a width of a non-action period of the energy voltage regulator are determined based on comparison of the reference current command signal and the reference upper current signal;
if the current command generator determines that the reference current command signal is higher than the reference upper current signal, then the current command generator generates a second current command signal to the switch controller according to the reference current command signal, the switch controller controls the switch circuit to perform continuous conduction control and thus the energy voltage regulator is operated under a continuous conduction state;
the second current command signal generated by the discontinuous conduction controller includes an action period parameter, a non-action period parameter and a number of conduction times parameter;
the action period parameter represents the width of the action period of a plurality of internal switches of the energy voltage regulator;
the non-action period parameter represents the width of the non-action period of the internal switches of the energy voltage regulator; and
the number of conduction times parameter represents a number of conduction times within a half cycle of the AC output signal.

7. The energy voltage regulator according to claim 6, wherein:
the switch controller compares the first or the second current command signal with a feedback current signal to obtain a switching signal, which controls switching of the plurality of internal switches of the switch circuit of the energy voltage regulator;
wherein, the feedback current signal is related to the AC output signal detected within the current cycle.

8. The energy voltage regulator according to claim 6, wherein:
the current command generator detects a converted AC output current and a converted AC output voltage within the current cycle to generate the reference current command signal.

9. The energy voltage regulator according to claim 6, wherein:
the reference upper current signal is related to a full-load AC output current.

10. The energy voltage regulator according to claim 6, wherein:
the switch controller controls the internal switches of the switch circuit to switch at least once within the width of the action period according to the first current command signal; and
the switch controller controls the internal switches of the switch circuit not to switch at all within the width of the non-action period according to the first current command signal.