TW201534020A - Inverting apparatus and detection method for islanding - Google Patents

Abstract

An inverting apparatus and a detection method for islanding are provided. The inverting apparatus includes a inverting circuit and a control circuit. The inverting circuit is coupled to a power grid and receives a direct current (DC) input power and converts the DC input power into an alternating current (AC) output voltage and an AC output current. The control circuit is coupled to the inverting circuit and configured to control power conversion of the inverting circuit. The control circuit generates a disturbance signal in a preset time interval to disturb the AC output current generated by the inverting circuit, and detects frequency of the AC output voltage to determine whether the frequency of the AC output voltage is within a preset frequency range, so as to determine whether to enable a islanding protection mechanism.

Description

Inverter device and method for detecting island operation

The invention relates to a power conversion technology, and in particular to an inverter device and a method for detecting an island operation.

In order to reduce the consumption rate of petrochemical energy, today's power systems are actively developing the application of renewable energy. In existing applications, the grid-connected AC power distribution system is the mainstream trend of today's power system development. The grid-connected AC power distribution system can use renewable energy such as solar power generation and wind power generation as a small distributed power system. The distributed power system is connected to the power grid to jointly supply power to the load device at the back end.

However, an existing and inevitable problem with such AC power distribution systems is that distributed power systems often experience island operations. More specifically, under such an AC power distribution system, the grid disconnects the inverter device of the distributed power system and the load device at the back end when the power supply is abnormal or during maintenance, thereby isolating the communication. Outside the power distribution system. At this time, if the inverter does not detect that the grid has been isolated from the AC power distribution system and continuously supplies power to the load device continuously, then this The phenomenon is generally called island operation. In the case of island operation, the power supply provided by the distributed power system is relatively unstable, which may cause damage to the load device.

The invention provides an inverter device and a method for detecting an island operation, which can accurately detect whether an inverter device is in an island operation.

The inverter device of the present invention includes an inverter circuit and a control circuit. The inverter circuit is connected to the power grid, wherein the inverter circuit receives the DC input power and converts the DC input power into an AC output voltage and an AC output current. The control circuit is coupled to the inverter circuit for controlling power conversion of the inverter circuit, wherein the control circuit generates a disturbance signal at a preset time interval to disturb the AC output current generated by the inverter circuit, and detects whether the frequency of the AC output voltage is Located within the preset frequency range to determine whether to enable the island protection mechanism.

In an embodiment of the invention, the control circuit determines whether the frequency of the AC output voltage is within a preset frequency range according to a voltage zero period of the AC output voltage.

In an embodiment of the invention, the current period of the AC output current is controlled by the disturbance signal; when the grid is operating normally and is connected to the inverter circuit, the voltage zero period is not affected by the fluctuation of the current period, and when the grid When an abnormality occurs and is disconnected from the inverter circuit, the voltage zero period changes with the fluctuation of the current period.

In an embodiment of the invention, the inverter circuit is responsive to the generation of the disturbance signal And adjust its power conversion behavior to shorten or extend the current cycle.

In an embodiment of the invention, the inverter circuit stops the power conversion in response to the generation of the disturbance signal, thereby shortening the current period.

In an embodiment of the invention, the control circuit includes a zero voltage detecting unit, a frequency detecting unit, a protection unit, and a driving control unit. The zero voltage detecting unit is coupled to the output end of the inverter circuit for detecting the zero voltage time point of the AC output voltage. The frequency detecting unit is coupled to the zero voltage detecting unit for calculating the voltage zero period according to the zero voltage time point of the AC output voltage. The protection unit is coupled to the frequency detecting unit for determining whether the frequency of the AC output voltage is within a preset frequency range according to the voltage zero period, and issuing a protection signal when the frequency of the AC output voltage is not within the preset frequency range. The driving control unit is coupled to the protection unit for enabling the island protection mechanism according to the protection signal, thereby controlling the operation of the inverter circuit.

The detecting method of the islanding operation of the invention is applicable to an alternating current power distribution system, wherein the alternating current power distribution system comprises an inverter device and a power grid, and the inverter device and the power grid are mutually connected, and the detecting method comprises the following steps: receiving the DC input power source by the inverter device The inverter input device converts the DC input power into an AC output voltage and an AC output current; generates a disturbance signal at a preset time interval to disturb the AC output current generated by the inverter device; and detects whether the frequency of the AC output voltage is at a preset Within the frequency range; and when the frequency of the AC output voltage is not within the preset frequency range, it is determined that the inverter device is islanding.

In an embodiment of the invention, the step of detecting whether the frequency of the AC output voltage is in the preset frequency range comprises: detecting the zero voltage time of the AC output voltage Point; calculate the voltage zero period according to the zero voltage time point of the AC output voltage; and determine whether the frequency of the AC output voltage is within the preset frequency range according to the voltage zero period.

In an embodiment of the invention, the step of generating a disturbance signal at a preset time interval to disturb the AC output current generated by the inverter device comprises: causing the inverter circuit to adjust the power conversion behavior of the disturbance signal in response to the disturbance signal, thereby shortening or prolonging the current cycle.

In an embodiment of the invention, the step of causing the inverter circuit to adjust its power conversion behavior by the disturbance signal, thereby shortening or extending the current period includes: causing the inverter circuit to stop the power conversion by reacting to the disturbance signal, thereby shortening the current period.

In an embodiment of the present invention, the method for detecting an island operation further includes the following steps: when determining that the inverter device has an islanding phenomenon, the island protection mechanism is enabled.

Based on the above, an embodiment of the present invention provides an inverter device and a method for detecting an island operation. The inverter device can determine whether the inverter device has an islanding operation by periodically disturbing the AC output current and detecting whether the AC output voltage changes accordingly, so as to be accurately enabled when the island operation occurs. The island protection mechanism prevents damage to the load device at the back end.

The above described features and advantages of the invention will be apparent from the following description.

10‧‧‧AC power distribution system

100‧‧‧Inverter

110‧‧‧Inverter circuit

120‧‧‧Control circuit

122‧‧‧ Zero voltage detection unit

124‧‧‧Frequency detection unit

126‧‧‧protection unit

128‧‧‧Drive Control Unit

DCin‧‧‧DC input power supply

EG‧‧‧ grid

I _AC ‧‧‧AC output current

LD‧‧‧ load device

Pz, p1, p1'‧‧‧ voltage zero period

S210~S260‧‧‧Steps for detecting the operation of isolated islands

Sc‧‧‧ control signal

Sd‧‧‧ disturbance signal

Tz, t0, t1, t2, td‧‧‧ zero voltage time point

V _AC ‧‧‧AC output voltage

1 is a schematic diagram of an AC power distribution system and an inverter device according to an embodiment of the present invention.

2 is a flow chart showing the steps of a method for detecting an island operation according to an embodiment of the present invention.

FIG. 3 is a functional block diagram of a control circuit according to an embodiment of the present invention.

4A is a schematic diagram showing voltage waveforms of an AC output voltage when no islanding operation occurs according to an embodiment of the present invention.

4B is a schematic diagram showing voltage waveforms of an AC output voltage when an islanding operation occurs according to an embodiment of the present invention.

In order to make the disclosure of the present disclosure easier to understand, the following specific embodiments are examples of the disclosure that can be implemented. In addition, wherever possible, the same elements, components, and steps in the drawings and embodiments are used to represent the same or similar components.

1 is a schematic diagram of an AC power distribution system and an inverter device according to an embodiment of the present invention. Referring to FIG. 1, the inverter device 100 of the present embodiment can be applied to the AC power distribution system 10. In the AC power distribution system 10 of the present embodiment, the input end of the inverter device 100 is coupled to a DC power generation device such as a photovoltaic module (not shown), a wind power generation component, or a hydropower component (for example, a regenerative power generation component). And the output of the inverter device 100 is connected to the grid EG. The inverter device 100 and the front-end renewable energy power generation component can be regarded as a distributed power supply system. in In FIG. 1, although only one distributed power supply system is illustrated as an example, the present invention is not limited thereto. In practical applications, the AC power distribution system 10 can also include multiple parallel distributed power systems.

The inverter device 100 can receive the DC input power source DCin from the front end photovoltaic module and convert the received DC input power source DCin into an AC output voltage V _AC and an AC output current I _AC . Specifically, the inverter device 100 includes an inverter circuit 110 and a control circuit 120. The inverter circuit 110 receives the DC input power source DCin and converts the DC input power source into an AC output voltage V _AC and an AC output current I _AC . The circuit configuration of the inverter circuit 110 can be, for example, a half bridge asymmetric, a half bridge symmetric, a full bridge or other feasible inverter circuit configuration, which is not limited by the present invention.

The control circuit 120 is coupled to the inverter circuit 110 for controlling the power conversion of the inverter circuit 110. The control signal Sc can be, for example, a PWM signal for controlling the switching period of the inverter circuit 110. However, the invention is not limited thereto.

In the AC power distribution system 10 of the present embodiment, the inverter device 100 and the front-end regenerative power generation component can be regarded as a distributed power system, which is connected in parallel with the grid EG and/or other distributed power systems (not shown) to The common power supply is used by the load device LD. In order to enable the inverter device 100 to accurately detect the occurrence of an island operation, and thereby perform a corresponding island protection mechanism, the inverter device 100 will periodically detect the output AC output current I _AC . The way of measuring the AC output voltage V _AC is to determine whether or not an islanding operation has occurred based on a change in the AC output voltage V _AC . The specific island operation detection method is shown in Figure 2. 2 is a flow chart of steps of a method for detecting an island operation according to an embodiment of the present invention.

Referring to FIG. 1 and FIG. 2 simultaneously, in the embodiment, first, the inverter circuit 110 receives the DC input power source DCin (step S210), and then converts the DC input power source DCin into an AC output voltage V _AC and an AC output current I. _AC (step S220). Then, the control circuit 120 generates a disturbance signal at a predetermined time interval to adjust the control signal Sc, thereby disturbing the AC output current I _AC generated by the inverter circuit 110 (step S230), and further detecting the output of the inverter circuit 110. Whether the frequency of the AC output voltage V _AC is within the preset frequency range (step S240).

When the control circuit 120 detects that the frequency of the AC output voltage V _AC is still within the preset frequency range, it means that the AC output voltage V _{AC is} still clamped by the voltage of the grid EG, and the frequency variation does not occur due to the disturbance of the current. Therefore, the control circuit 120 determines that the inverter device 100 does not currently have an islanding operation (step S250), that is, the power grid EG should be in a normal operating state at this time and is connected to the inverter circuit 110.

Conversely, when the control circuit 120 detects that the frequency of the AC output voltage V _AC has exceeded the preset frequency range, it means that the AC output voltage V _AC is not clamped by the voltage of the grid EG, but is disturbed by the current. The frequency change occurs, so the control circuit 120 determines that the inverter device 100 has an islanding operation (step S260), that is, the power grid EG has been isolated from the alternating current power distribution system 10 at this time.

After detecting whether the inverter device 100 has an islanding operation, the control circuit 120 can determine whether to enable the island protection mechanism to control the operation of the inverter circuit 110, thereby avoiding damage of the load device LD at the back end. For example, the inverter circuit 110 can include a protection relay (not shown). When the control circuit 120 determines When the islanding operation occurs and the island protection mechanism is enabled, the control circuit 120 enables the protection of the power, so that the inverter device 100 is disconnected from other parts of the AC power distribution system 10 (for example, the load device LD) to avoid the operation of the island. It continues to happen.

In detail, the control circuit 120 can generate, for example, four disturbance signals in every 40 AC output voltages V _AC cycles (not limited thereto, and can be adjusted according to the designer's needs) to disturb the output control signal Sc, so that the inverter The circuit 110 reacts with the control signal Sc to cause the current period of the generated AC output current I _AC to change accordingly. More specifically, the inverter circuit 110 can adjust its power conversion behavior in response to the generation of the disturbance signal, thereby shortening or extending the current period of the AC output current I _AC . For example, the inverter circuit 110 can stop the power conversion in response to the generation of the disturbance signal, so that the current period of the AC output current I _AC is shortened.

When the grid EG is operating normally and is connected to the inverter circuit 110 (ie, when islanding does not occur), the voltage zero period of the AC output voltage V _AC is clamped to a specific frequency by the voltage output by the grid EG (for example, 60 Hz) without being affected by variations in the current period of the AC output current I _AC . On the other hand, when the grid EG is abnormal and disconnected from the inverter circuit 110, the voltage zero period of the AC output voltage V _AC changes with the fluctuation of the current period due to the lack of clamping of the grid voltage.

With this feature, control circuit 120 can detect the use of the AC output voltage V _AC voltage zero cycle AC output voltage V _AC is determined whether the frequency is within a predetermined frequency range, thereby accurately determine whether the inverter device 100 An island operation occurred.

The following is an example of a specific architecture illustrated in FIG. 3 and a voltage waveform of the AC output voltage V _AC illustrated in FIGS. 4A and 4B to illustrate how the control circuit 120 implements the above-described island operation detection mechanism. FIG. 3 is a functional block diagram of a control circuit according to an embodiment of the present invention. 4A and FIG. 4B are schematic diagrams showing voltage waveforms of an AC output voltage when no islanding operation occurs, according to an embodiment of the present invention.

Referring to FIG. 3 and FIG. 4A simultaneously, in the embodiment, the control circuit 120 includes a zero voltage detecting unit 122, a frequency detecting unit 124, a protection unit 126, and a driving control unit 128. The zero voltage detecting unit 122 is coupled to the output end of the inverter circuit 110 for detecting the zero voltage time point tz of the AC output voltage V _AC . The zero voltage time point tz is, for example, the time points t2 and td in FIGS. 4A and 4B.

The frequency detecting unit 124 is coupled to the zero voltage detecting unit 122 for calculating the voltage zero period pz according to the zero voltage time point tz of the AC output voltage V _AC . The voltage zero period period pz is, for example, the periods p1 and p1' in FIGS. 4A and 4B.

The protection unit 126 is coupled to the frequency detecting unit 124 to receive the voltage zero period pz calculated by the frequency detecting unit 124. In this embodiment, the protection unit 126 determines whether the voltage zero period period pz is within the preset frequency range, and then sends a protection signal Sp to the drive control unit 128 according to the result of the determination. When the protection unit 126 determines that the frequency of the AC output voltage V _AC is outside the preset frequency range according to the received voltage zero period pz, the driving control unit 128 adjusts the control signal Sc output by the protection signal Sp according to the protection signal Sp. Enable the island protection mechanism.

In terms of the overall control behavior of the control circuit 120, first, when the disturbance control signal Sd is not generated by the drive control unit 128, the drive control unit 128 generates a control signal Sc to control the inverter circuit 110 to operate normally. At this time, the AC output voltage V _AC generated by the inverter circuit 110 basically has a voltage waveform with a voltage period of p1.

When the preset time interval is reached, the drive control unit 128 generates a disturbance signal Sd to disturb the control signal Sc. The inverter circuit 110 stops the power conversion during the time point td-t2 in response to the disturbed control signal Sc. If there is no island operation at this time, please refer to FIG. 4A, although the AC output current I _AC is set to 0A at the time point td, since the waveform of the AC output voltage V _AC is clamped by the grid voltage, the AC is exchanged. The voltage waveform of the output voltage V _AC during the time point td-t2 is maintained in the original sine wave form, gradually changing from the negative voltage toward the zero voltage. In this case, the zero voltage detecting unit 122 detects that the zero voltage time point of the AC output voltage V _AC is t2, so that the frequency detecting unit 124 calculates the voltage zero period as p1. Therefore, the protection unit 126 determines that the frequency of the AC output voltage V _AC is within the preset frequency range according to the voltage zero period p1, so that the drive control unit 128 does not enable the island protection mechanism.

On the other hand, if the inverter device 100 is in an islanding operation at this time, referring to FIG. 4B, the AC output voltage V _AC is reflected in the stop operation of the inverter circuit 110 at the time point td-t2 (AC output current I _AC It is set to 0A), and the voltage waveform at which the voltage value is pulled down to zero voltage at the time point td is presented. In this case, the zero voltage detecting unit 122 detects the zero voltage time point of the AC output voltage V _AC as td, so that the frequency detecting unit 124 calculates the voltage zero period as p1'. Therefore, the protection unit 126 determines that the frequency of the AC output voltage V _AC is outside the preset frequency range according to the voltage zero period p1', so that the drive control unit 128 activates the protection signal Sp to enable the island protection mechanism.

In summary, the embodiment of the present invention provides an inverter device and a method for detecting an island operation. The inverter device can determine whether the inverter device has an islanding operation by periodically disturbing the AC output current and detecting whether the AC output voltage changes accordingly, so as to be accurately enabled when the island operation occurs. The island protection mechanism prevents damage to the load device at the back end.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and any one of ordinary skill in the art can make some changes and refinements without departing from the spirit and scope of the present invention. The scope of the invention is defined by the scope of the appended claims.

S210~S260‧‧‧Steps for detecting the operation of isolated islands

Claims (12)

An inverter device includes: an inverter circuit coupled to a power grid, wherein the inverter circuit receives a DC input power source, and converts the DC input power source into an AC output voltage and an AC output current; and a control a circuit coupled to the inverter circuit for controlling power conversion of the inverter circuit, wherein the control circuit generates a disturbance signal at a predetermined time interval to disturb the AC output current generated by the inverter circuit, and detects The frequency of the AC output voltage is measured within a predetermined frequency range to determine whether an island protection mechanism is enabled. The inverter device of claim 1, wherein the control circuit determines whether the frequency of the AC output voltage is within the preset frequency range according to a voltage zero period of the AC output voltage. The inverter device of claim 2, wherein a current period of the alternating current output current is controlled by the disturbance signal; and when the power grid is normally operated and is connected to the inverter circuit, the voltage zero point The period is unaffected by variations in the current period, and when an abnormality occurs in the grid and is disconnected from the inverter circuit, the voltage zero period changes as the current period fluctuates. The inverter device of claim 3, wherein the inverter circuit adjusts its power conversion behavior in response to the generation of the disturbance signal, thereby shortening or extending the current period. The inverter device of claim 4, wherein the inverter circuit The power conversion is stopped in response to the generation of the disturbance signal, thereby shortening the current period. The inverter device of claim 1, wherein the control circuit comprises: a zero voltage detecting unit coupled to the output end of the inverter circuit for detecting a zero voltage time point of the AC output voltage a frequency detecting unit coupled to the zero voltage detecting unit for calculating a voltage zero period according to the zero voltage time point of the AC output voltage; a protection unit coupled to the frequency detecting unit for The voltage zero period determines whether the frequency of the AC output voltage is in the preset frequency range, and sends a protection signal when the frequency of the AC output voltage is not within the preset frequency range; and a driving control unit coupled to the protection The unit is configured to enable the island protection mechanism according to the protection signal to control the operation of the inverter circuit. The method for detecting an island operation is applicable to an AC power distribution system, wherein the AC power distribution system includes an inverter device and a power grid, and the inverter device and the power grid are mutually connected, and the detecting method includes: borrowing the inverter Receiving, by the inverter device, the DC input power source is converted into an AC output voltage and an AC output current; generating a disturbance signal at a predetermined time interval to disturb the AC generated by the inverter device Output current; detecting whether the frequency of the AC output voltage is within a predetermined frequency range; And when the frequency of the AC output voltage is not within the preset frequency range, determining that the inverter device has an island operation phenomenon. The method for detecting an island operation according to claim 7, wherein the step of detecting whether the frequency of the AC output voltage is in the preset frequency range comprises: detecting a zero voltage time point of the AC output voltage; The zero voltage time point of the AC output voltage calculates a voltage zero period; and determines whether the frequency of the AC output voltage is within the preset frequency range according to the voltage zero period. The method for detecting an island operation according to claim 8, wherein a current period of the alternating current output current is controlled by the disturbance signal; when the power grid is normally operated and is connected to the inverter circuit, The voltage zero period is not affected by variations in the current period, and when an abnormality occurs in the grid and is disconnected from the inverter circuit, the voltage zero period changes as the current period fluctuates. The method for detecting an island operation according to claim 9 , wherein the step of generating the disturbance signal at the preset time interval to disturb the AC output current generated by the inverter device comprises: causing the inverter circuit Reacting to the disturbance signal adjusts its power conversion behavior to shorten or extend the current period. The method for detecting an island operation as described in claim 10, The step of causing the inverter circuit to adjust its power conversion behavior in response to the disturbance signal, thereby shortening or extending the current period includes: causing the inverter circuit to stop the power conversion in response to the disturbance signal, thereby shortening the current period. The method for detecting an island operation according to claim 7 of the patent application scope further includes: when determining that the islanding operation phenomenon occurs in the inverter device, enabling an island protection mechanism.