Patent Description:
A photovoltaic power optimizer is usually connected to an inverter by using a plurality of converters that are connected in series, and different optimizers are usually connected to each other by connecting outputs in parallel, to increase input power.

The plurality of converters in the photovoltaic power optimizer are respectively connected to different photovoltaic panels. When a photovoltaic panel needs maintenance, a maintenance worker disconnects an input terminal of a corresponding converter. However, in this case, an output voltage of another optimizer that is connected to this optimizer by connecting outputs in parallel impacts a corresponding converter of the photovoltaic panel, thereby damaging a component inside the converter.

<CIT> discloses a non-isolated (transformerless) direct current-to-direct current (DC-DC) power supply which includes a voltage converter module that converts DC input voltage having a first voltage level into a DC output having a second voltage level that is less than the first voltage level. If the output voltage rises to an overvoltage threshold, internal overvoltage module immediately opens a top magnetizing MOSFET and closes a bottom synchronous MOSFET, thereby crowbarring the output.

<CIT> discloses a method for operating a maximum power point tracing (MPPT) controller including a switching circuit adapted to transfer power between an input port and an output port.

<CIT> discloses an electric power system which includes N electric power sources and N switching circuits, where N is an integer greater than one.

This application provides a serial-parallel converter protection system, a conversion control method, and a converter, as defined in the appended set of claims. The converter is bypassed when a voltage is excessively large, thereby preventing the voltage and a current from impacting a component inside the converter.

In this application, when the output voltage of the converter is greater than the first threshold, the controller controls the first switching transistor to be turned off and controls the second switching transistor to be turned on, so that the converter is bypassed, thereby preventing a voltage and a current from impacting a component inside the converter.

After the controller controls the second switching transistor to be turned off, the converter is reconnected to a power grid (exits a bypass state). If the output voltage of the converter returns to be normal, the converter operates normally. In some implementations, the controller may first control the first switching transistor to be turned on and control the second switching transistor to be turned off, and then perform re-detection.

Embodiments of this application provide a serial-parallel converter protection system, a controller, and a converter. The converter is bypassed when a voltage is excessively large, thereby preventing the voltage and a current from impacting a component inside the converter.

In this specification, the claims, and the accompanying drawings of this application, terms "first", "second", "third", "fourth", and the like (if existent) are intended to distinguish between similar objects but do not necessarily indicate a specific order or sequence. It should be understood that the data termed in such a way is interchangeable in proper circumstances, so that embodiments of this application described herein can be implemented in other orders than the order illustrated or described herein. Moreover, terms "include", "correspond to", and any other variants thereof mean to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a list of steps or units is not necessarily limited to those steps or units, but may include other steps or units not expressly listed or inherent to such a process, method, product, or device.

In addition, in embodiments of this application, the word "example" or "for example" is used to represent giving an example, an illustration, or a description. Any embodiment or design scheme described as the word "example" or "for example" in embodiments of this application should not be explained as being more preferred or having more advantages than another embodiment or design scheme. Exactly, use of the word "example" or "for example" or the like is intended to present a relative concept in a specific manner.

<FIG> is a schematic diagram of serial-parallel converters connected to an inverter. After being connected in parallel, a first optimizer <NUM> and a second optimizer <NUM> are connected to an inverter <NUM>. The first optimizer <NUM> includes a plurality of converters <NUM> connected in series, and an input terminal of each converter <NUM> may be connected to a photovoltaic panel <NUM>. Two output terminals are formed after output terminals of the converters <NUM> are connected in series in a manner shown in <FIG>, and the two output terminals are used as output terminals of the first optimizer <NUM>.

An internal structure of the second optimizer <NUM> may be similar to that of the first optimizer <NUM> and is not drawn in detail in <FIG>, and details are not described herein again. In some other cases, the second optimizer <NUM> may alternatively have another internal structure. This is not limited in this embodiment of this application.

In the first optimizer <NUM>, the photovoltaic panel <NUM> may be an apparatus for converting solar energy into electric power. A specific model, a mounting manner, an area, and the like of the photovoltaic panel are not limited in this embodiment of this application. In another new energy power generating system or an energy storage system, the photovoltaic panel <NUM> may be replaced with a corresponding apparatus. For example, in a wind energy power generating system, the photovoltaic panel <NUM> may be replaced with a wind-driven generator. For another example, in an energy storage system, the photovoltaic panel <NUM> may be replaced with an energy storage battery. In actual application, the photovoltaic panel <NUM> may be replaced with a different apparatus according to an actual requirement, and is connected to a converter <NUM>. Details are not described in this embodiment of this application.

In the first optimizer <NUM>, the converter <NUM> may be a direct current-direct current converter. In actual application, the converter <NUM> may alternatively be another type of converter. This is not limited in this embodiment of this application.

<FIG> is a schematic diagram of an internal structure of the converter <NUM>. The internal structure of the converter <NUM> may include a switching transistor Q1, a switching transistor Q2, a capacitor C1, a capacitor C2, and an inductor L. The capacitor C1 is connected in parallel between an input terminal <NUM> and an input terminal <NUM> of the converter, and the capacitor C2 is connected in parallel between an output terminal <NUM> and an output terminal <NUM> of the converter. The switching transistor Q1 and the inductor L are connected in series between the input terminal <NUM> and the output terminal <NUM>. The switching transistor Q2 is connected in parallel between the output terminal <NUM> and a connection terminal of the switching transistor Q1 and the inductor L.

The switching transistor Q1 or the switching transistor Q2 may be a triode, a MOS transistor, or a transistor of another type in actual application, for example, an insulated gate bipolar transistor (insulated gate bipolar transistor, IGBT). This is not limited in this embodiment of this application. In some embodiments, the switching transistor Q1 and the switching transistor Q2 each may be anti-parallel with a diode.

With reference to <FIG>, when a first photovoltaic panel <NUM> of the first optimizer <NUM> needs maintenance or replacement, a worker disconnects an input terminal of a corresponding converter <NUM>. In this case, an output voltage of the second optimizer <NUM> impacts the converter <NUM>, thereby damaging a component (for example, a capacitor or a switching transistor) inside the converter. In <FIG>, a line <NUM> is a current path before the worker disconnects the input terminal of the corresponding converter <NUM>, and a line <NUM> is a current path after the worker disconnects the input terminal of the corresponding converter <NUM>. It can be learned that after the worker disconnects the input terminal of the corresponding converter <NUM>, a current and a voltage are applied to an input capacitor, and the capacitor is damaged. In some cases, the current and the voltage may further impact the switching transistor Q2, and the switching transistor Q2 is damaged.

To resolve the foregoing technical problem, this application provides a serial-parallel converter protection system, as shown in <FIG> is a schematic diagram of a serial-parallel converter protection system according to this application. The serial-parallel converter protection system includes: a controller <NUM>, a drive <NUM>, a switching transistor Q1, and a switching transistor Q2. A connection relationship of the switching transistor Q1, the switching transistor Q2, an input capacitor, an output capacitor, an inductor, and the like is similar to that of the corresponding converter in <FIG>, and details are not described herein again. In addition the input terminal of the converter is connected to the output terminal of the converter through the switching transistor Q1, and the controller <NUM> is connected to the switching transistor Q1 through the drive <NUM> and is configured to control on and off of the switching transistor Q1. The output terminal of the converter is connected in parallel with the switching transistor Q2, and the controller <NUM> is connected to the switching transistor Q2 through the drive <NUM> and is configured to control on and off of the switching transistor Q2.

In this embodiment of this application, when an output voltage Vo of the converter is greater than a first threshold, the controller controls the switching transistor Q1 to be turned off and controls the switching transistor Q2 to be turned on. That the output voltage Vo of the converter is greater than the first threshold shows that a voltage of the output terminal of the converter is high and damages a component inside the converter. Therefore, in this case, the controller <NUM> may control the switching transistor Q1 to be turned off and control the switching transistor Q2 to be turned on, so that a current path is short-circuited through the switching transistor Q2 instead of the switching transistor Q1 and is output to another output terminal. Actually, the converter <NUM> is bypassed, thereby avoiding damage to the converter, and resolving a technical problem that the converter is damaged when the output voltage is excessively high.

<FIG> is a schematic diagram of a current path in a protection process according to an embodiment of this application. As shown in <FIG>, after the controller <NUM> controls the switching transistor Q1 to be turned off and controls the switching transistor Q2 to be turned on, the current path flows through the switching transistor Q2 in the converter <NUM> (as shown by a line <NUM> in <FIG>), and the converter <NUM> is bypassed.

In actual application, the controller <NUM> may detect the output voltage Vo through a voltage detection unit <NUM>. Specifically, the voltage detection unit <NUM> may be a circuit or component that can detect a voltage, for example, a voltage sensor. This is not limited in this embodiment of this application.

In actual application, the controller <NUM> may control the switching transistor Q1 and the switching transistor Q2 through the drive <NUM>. Specifically, the drive <NUM> may be a drive circuit that is configured to receive a control signal of the controller <NUM>, convert the control signal into a corresponding high/low level, and output the level to the switching transistor Q1 and the switching transistor Q2, thereby controlling on and off of both the switching transistor Q1 and the switching transistor Q2. In this embodiment of this application, a circuit or a structure of the drive <NUM> is not limited.

In some cases, an auxiliary power supply <NUM> provides electric energy for the controller <NUM> and the drive <NUM>. An input terminal of the auxiliary power supply <NUM> is connected in parallel with the input terminal of the converter, and is configured to obtain electric energy. The auxiliary power supply <NUM> is further connected to the controller <NUM> and the drive <NUM>, and is configured to output the obtained electric energy to the controller <NUM> and the drive <NUM>.

After the controller controls the switching transistor Q1 to be turned off and controls the switching transistor Q2 to be turned on, an input voltage Vin and the output voltage Vo of the converter decrease. When the input voltage Vin of the converter decreases to a second threshold, the auxiliary power supply <NUM> may not obtain enough electric energy. Therefore, when the input voltage Vin of the converter decreases to the second threshold, the controller <NUM> may control both the switching transistor Q1 and the switching transistor Q2 to be turned off. As a result, a current of the second optimizer <NUM> continues to flow to the input terminal of the converter through a diode anti-parallel with the switching transistor Q1. In this way, the input voltage Vin of the converter increases, to maintain the power supply of the auxiliary power supply.

In this embodiment of this application, through control logic of the controller <NUM>, when the output voltage of the converter is excessively high, the switching transistor Q2 can be controlled to bypass the converter, to prevent an excessively high voltage from damaging a component inside the converter. On the other hand, when the input voltage of the converter is excessively low, the switching transistor Q2 can be controlled to be turned off, so that electric energy can continue to flow to the input terminal of the converter, thereby maintaining normal operation of the controller <NUM> and the drive <NUM>, and implementing continuous protection of the converter.

After a worker maintains or replaces a photovoltaic panel <NUM>, a corresponding converter <NUM> may be reconnected by the worker. In this case, the worker may input instructions to enable the controller <NUM> to control the switching transistor Q1 to be turned on and the switching transistor Q2 to be turned off, so that the converter <NUM> resumes normal operation. When the worker does not input the instructions, the controller <NUM> may perform timing after detecting for the first time that the output voltage Vo of the converter is greater than the first threshold. When the timing reaches a preset time threshold, the controller <NUM> re-detects the output voltage Vo of the converter. If the output voltage Vo of the converter is less than the first threshold, the controller <NUM> may control the switching transistor Q1 to be turned on and the switching transistor Q2 to be turned off, so that the converter <NUM> resumes normal operation. In this case, after the photovoltaic panel <NUM> is reconnected to the converter by the worker, the controller <NUM> can automatically control the converter to resume normal operation, which is more automatic without operation of the worker.

Based on the foregoing control logic, the controller <NUM> may perform steps shown in <FIG> is a flowchart of a protection policy method of a controller <NUM> according to an embodiment of this application. The process includes the following steps.

<NUM>: Detect an output voltage of a converter.

In this embodiment of this application, the controller <NUM> may detect the output voltage Vo of the converter through a voltage detection unit <NUM>. This is similar to the description of the foregoing embodiment, and details are not described herein again.

<NUM>: If the output voltage of the converter is greater than a first threshold, perform overvoltage protection, and start timing.

In this embodiment of this application, the overvoltage protection may include following control logic:.

In actual application, the foregoing control logic may be directly performed in the controller, or a related procedure (an overvoltage protection procedure) may be set to implement the foregoing logic. This is not limited in this embodiment of this application.

For example, the overvoltage protection may perform steps as shown in <FIG>, and for details, refer to a subsequent embodiment.

The overvoltage protection may control the output voltage Vo of the converter in a reasonable range, and maintain the input voltage Vin of the converter, to prevent power shortage of an auxiliary power supply <NUM>. Therefore, when a worker replaces or maintains a photovoltaic panel <NUM>, the overvoltage protection may prevent damage to a component inside the converter due to an excessively high voltage.

<NUM>: If counted time reaches a preset time threshold, exit the overvoltage protection procedure, and return to perform step <NUM>.

In this embodiment of this application, the controller <NUM> may count time by using a timer. When the time counted by the timer reaches the preset time threshold, the controller <NUM> may exit the overvoltage protection procedure (or may control the switching transistor Q2 to be turned off, so that the converter is not bypassed), and then re-detect the output voltage of the converter. In some embodiments, after the controller <NUM> exits the overvoltage protection procedure, both the switching transistor Q1 and the switching transistor Q2 may be turned off, and step <NUM> is performed again (that is, re-detect the output voltage of the converter). It may be understood that, after a period of time, the worker may have completed the maintenance or replacement of the photovoltaic panel <NUM>, and reconnected the photovoltaic panel to the converter. Therefore, the converter is re-detected at regular intervals, so that restoration of normal operation can be implemented after the photovoltaic panel <NUM> is reconnected to the converter.

<NUM>: If the output voltage of the converter is not greater than the first threshold, operate the converter normally.

In this embodiment of this application, if the photovoltaic panel <NUM> is not removed and the worker does not disconnect an input interface of the converter, the output voltage Vo of the converter may be in a normal operating state, and does not exceed the first threshold, so the converter operates normally. In may be understood that the controller <NUM> may control both the switching transistor Q1 and the switching transistor Q2 to return to work normally, so that the converter returns to operate normally. In some embodiments, the controller may control the switching transistor Q1 to be turned on and control the switching transistor Q2 to be turned off, so that the converter returns to operate normally.

The foregoing steps of the overvoltage protection may be directly performed by the controller <NUM>, or may be performed by an overvoltage protection unit <NUM> inside the controller <NUM>. The overvoltage protection unit <NUM> is a logic module inside the controller <NUM> and may include a microprocessor and a memory. The memory stores instructions, and the microprocessor reads the instructions to perform the steps of the overvoltage protection. The steps of the overvoltage protection may be as shown in <FIG> is a flowchart of the steps of the overvoltage protection according to an embodiment of this application. The process includes the following steps.

<NUM>: Detect the input voltage Vin and the output voltage Vo of the converter.

In this embodiment of this application, the controller <NUM> may separately detect the input voltage Vin and the output voltage Vo of the converter through the voltage detection unit <NUM>. This is similar to the description of the voltage detection unit <NUM> in the foregoing embodiment, and details are not described herein again.

<NUM>: Detect whether the output voltage Vo of the converter is greater than the first threshold Vth <NUM>, and perform step <NUM> if the output voltage Vo of the converter is greater than the first threshold Vth <NUM>, or perform step <NUM>, if the output voltage Vo of the converter is not greater than the first threshold Vth <NUM>.

In this embodiment of this application, when the controller detects that the output voltage Vo of the converter is greater than the first threshold Vth <NUM>, step <NUM> is performed (the switching transistor Q2 is turned on), so that the converter is bypassed. When the controller detects that the output voltage Vo of the converter is not greater than the first threshold Vth <NUM>, step <NUM> is performed (the switching transistor Q2 is turned off).

<NUM>: Turn on the switching transistor Q2.

In this embodiment of this application, when the controller <NUM> controls the switching transistor Q2 to be turned on through the drive <NUM>, a current received by the converter flows through the switching transistor Q2. In this case, the converter is bypassed, and a component inside the converter is not damaged.

In some cases, the controller may turn on the switching transistor Q2 and turn off the switching transistor Q1 at the same time, to prevent the current from impacting the input terminal of the converter. If the switching transistor Q1 is turned off, only the switching transistor Q2 may be turned on.

<NUM>: Detect whether the input voltage Vin of the converter is greater than the second threshold Vth <NUM>, and perform step <NUM> if the input voltage Vin of the converter is greater than the second threshold Vth <NUM>, or return to step <NUM> if the input voltage Vin of the converter is not greater than the second threshold Vth <NUM>.

In this embodiment of this application, that the input voltage Vin of the converter is less than the second threshold Vth <NUM> indicates that the input voltage will not continue to provide electric energy for the auxiliary power supply <NUM>. Therefore, the controller may perform step <NUM> to turn off the switching transistor Q2, so that the current may flow through the input terminal of the converter, and the input voltage Vin increases again.

<NUM>: Turn off the switching transistor Q2.

In this embodiment of this application, after the controller <NUM> turns off the switching transistor Q2, the current may be transmitted to the input terminal of the converter through a diode anti-parallel with the switching transistor Q1, so that the input voltage Vin increases again.

<FIG> is a voltage sequence diagram corresponding to the steps in <FIG>. At the beginning of t1 duration, the controller <NUM> detects that the output voltage Vo of the converter exceeds the first threshold Vth <NUM>. In this case, the switching transistor Q2 is turned on (and the switching transistor Q1 is turned off). Therefore, the converter is bypassed, and the input voltage and the output voltage of the converter decrease.

After the t1 duration, the input voltage Vin of the converter is less than the second threshold Vth <NUM>. In this case, the controller <NUM> may turn off the switching transistor Q2, so that the converter is not bypassed, the current may flow into the converter again, and the input voltage and the output voltage of the converter may increase.

After t2 duration, the output voltage of the converter is greater than the first threshold Vth <NUM>. In this case, the controller <NUM> may turn on the switching transistor Q2, so that the converter is bypassed, and the input voltage and the output voltage of the converter decrease.

In this embodiment of this application, the controller <NUM> turns on or off the switching transistor Q2 based on a specific condition of the input voltage and the output voltage of the converter, so that the input voltage and the output voltage of the converter circularly decrease and increase, and are always kept in a reasonable range. Therefore, no damage is caused to the component inside the converter, and a technical problem that the converter is damaged when the output voltage of the converter is excessive high is resolved.

In some other embodiments, the controller <NUM> may control the switching transistor Q2 to be turned on through pulse width modulation (pulse width modulation, PWM) chopping, as shown in <FIG>.

<FIG> is a corresponding sequence diagram when the controller <NUM> turns on the switching transistor Q2 through PWM chopping according to an embodiment of this application.

In the embodiment corresponding to <FIG>, the controller <NUM> turns on the switching transistor Q2 through PWM chopping. As shown in <FIG>, the switching transistor Q2 performs PWM based on a specific duty ratio. The duty ratio may be set based on an actual condition. This is not limited in this embodiment of this application.

In the embodiment corresponding to <FIG>, the controller <NUM> turns on the switching transistor Q2 through PWM chopping, to slow down the decrease of the output voltage Vo and the input voltage Vin of the converter, so that the controller <NUM> does not need to frequently switch a control state, to improve system stability. Another case of this embodiment is similar to that of the foregoing embodiments, and details are not described herein again.

The first threshold Vth <NUM>, the second threshold Vth <NUM>, the preset time threshold, and the like in each foregoing embodiment may be specifically set based on an actual condition. In this embodiment of this application, specific values of the foregoing thresholds are not limited.

An embodiment of this application further provides a converter, including a converter circuit. The converter circuit is similar to the circuit corresponding to <FIG>. An input terminal of the converter circuit is connected to at least one photovoltaic panel, and an output terminal of the converter circuit is connected to a power grid.

The converter may include the serial-parallel converter protection system shown in <FIG>. The serial-parallel protection system is connected to the converter circuit through a switching transistor Q1 and a switching transistor Q2, and is similar to that in <FIG>.

Alternatively, the converter may include a controller. The controller is similar to the controller <NUM> in the embodiment corresponding to <FIG>, and details are not described herein again. The controller may be connected to the switching transistor Q1 and the switching transistor Q2 through a drive. In some embodiments, the converter further includes an auxiliary power supply which is similar to the auxiliary power supply <NUM> in the embodiment corresponding to <FIG>.

It can be clearly understood by a person skilled in the art that, for a purpose of convenient and brief description, for detailed working processes of the foregoing system, apparatus, and unit, refer to corresponding processes in the foregoing method embodiments.

For example, the described apparatus embodiments are merely examples. For example, division into units is merely logical function division and may be other division during actual implementation. For example, a plurality of units or components may be combined or integrated into another system. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented through some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electrical, mechanical, or another form.

In addition, functional units in embodiments of this application may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units may be integrated into one unit.

Claim 1:
A serial-parallel converter protection system for a converter (<NUM>) of a first optimizer (<NUM>) connected with a second optimizer (<NUM>) in parallel, the first optimizer (<NUM>) comprising a plurality of converters connected in series which comprise the converter (<NUM>), wherein the serial-parallel converter protection system comprises a controller (<NUM>), a drive (<NUM>), a first switching transistor (Q1), a second switching transistor (Q2), and an auxiliary power supply (<NUM>), wherein
the auxiliary power supply (<NUM>) is connected in parallel with the input terminal of the converter (<NUM>), an input terminal of the converter (<NUM>) is connected to an output terminal of the converter (<NUM>) through the first switching transistor (Q1), and the controller (<NUM>) is connected to the first switching transistor (Q1) through the drive (<NUM>) and is configured to control on and off of the first switching transistor (Q1);
the output terminal of the converter (<NUM>) is connected in parallel with the second switching transistor (Q2), and the controller (<NUM>) is connected to the second switching transistor (Q2) through the drive (<NUM>) and is configured to control on and off of the second switching transistor (Q2); and
based on an output voltage of the converter (<NUM>) is greater than a first threshold (Vth1), the controller (<NUM>) is further configured to control the first switching transistor (Q1) to be turned off and control the second switching transistor (Q2) to be turned on,
wherein the first switching transistor (Q1) is anti-parallel with a first diode, and the second switching transistor (Q2) is anti-parallel with a second diode,
wherein when an input voltage of the converter (<NUM>) is less than a second threshold (Vth2), the controller (<NUM>) is further configured to control both the first switching transistor (Q1) and the second switching transistor (Q2) to be turned off, such that a current of the second optimizer (<NUM>) flows to the input terminal of the converter (<NUM>) through the first diode.