TWI418827B - Isolation operation detection method of electric current control type electric current converter - Google Patents

Description

Island operation detection method for commercial power-coupled current-controlled power converter

The invention relates to a method for detecting an island operation of a commercial parallel-type current-controlled power converter, in particular to a power balance between a power generated by a distributed power generation system and a total load or a power system failure. The output current of the current-controlled power converter is disturbed to determine whether or not an islanding operation detection method occurs.

Small-scale power generation systems or renewable energy power generation systems (such as solar power, wind power, fuel cell power generation, etc.) can be regarded as a decentralized power generation system. These distributed power generation systems can be connected in parallel to the mains power system to supply power to the load. Since the distributed power generation system operates in parallel with the mains power supply system, it must have relevant protection mechanisms to ensure the safety during operation. The "island operation" detection is one of the necessary protection mechanisms. The island operation detection system is formed when the mains power system is disconnected due to failure or maintenance, etc., and the distributed power generation system is continuously supplied with power. This island operation phenomenon will seriously damage the safety of the maintenance of the mains power system personnel and damage the power equipment.

Therefore, the following is a brief description of several related patent documents for detecting island operations. The Republic of China Invention Patent Bulletin No. I278635 discloses an active "island detection method" that utilizes a high-resolution measurement device to detect changes in the system voltage frequency and size by using the power system to perturb. Compare the difference between the front and back and adjust the function to determine an adjustment amount, as the next time to add a trace of the current output frequency or phase change amount, according to the system voltage magnitude and the system voltage frequency to determine whether islanding occurs. But this method The power system needs to be continuously disturbed, which has the disadvantage of affecting the power quality, and requires high-resolution measurement and measurement equipment, resulting in an increase in measurement cost.

Another example is the US Island Patent No. 7,275,002 (Islanding detection and protection method), which discloses a method of changing the negative phase sequence voltage to disturb the power system, detecting changes in the system voltage frequency to determine whether or not an island operation occurs, and when the power system is powered off. When the island is in operation, the voltage of the system voltage is shifted due to the injection of the negative phase sequence voltage, and the drift of the system voltage frequency is accelerated by the positive feedback method, thereby detecting the islanding operation. However, this method needs to change the negative phase sequence voltage to continuously disturb the power system, so it is only applicable to the three-phase power system, and the power system continues to be disturbed, thus affecting the power quality.

In the case of the device and methods for detecting islanding operation of a static power source, the power converter is first phase-locked with the mains voltage, and the voltage frequency generated by the power converter is slightly different from the mains voltage. Change, and judge the change of the voltage frequency and the previous voltage frequency. If it is not greater than the minimum frequency change, it means that the mains is normal, then the cycle of the output voltage of the power converter will be changed again every cycle; When the frequency and the previous voltage frequency change amount are greater than the set value of the minimum frequency change amount, the frequency change amount will be accumulated, and the next output voltage frequency variation amount will be added to the last time, and the mains frequency will be detected again if the mains frequency is normal. When the normal value range is exceeded, it indicates that island operation has occurred. However, this method is also a continuous disturbance to the power system, which will affect the power quality.

Due to the currently known active island operation detection method, it is required to The force system is continuously disturbed, which affects the power quality of the power system.

In view of this, the main object of the present invention is to provide an islanding operation detection method for a commercial parallel power-type current-controlled power converter, in which the power generated by the normal and distributed power generation system of the power system is not balanced with the power consumed by the total load. When the output current of the current-controlled power converter does not disturb the power system; conversely, the current-controlled power is only when the power generated by the distributed power generation system is balanced with the power consumed by the total load or the power system is faulty. The converter will perturb the power system to determine if islanding has occurred.

In order to achieve the foregoing objective, the islanding operation detecting method of the commercial parallel-type current-controlled power converter of the present invention comprises: connecting a distributed power generation system to a mains power supply, and supplying power to a load, wherein the distributed power generation system The utility model comprises a DC power and a current control type electric energy converter, which provides a real power to the mains power supply; the mains current of the mains power source is taken as an absolute value, and if the absolute value is greater than a preset error value, the mains is determined The power supply is normal, so that the current-controlled power converter does not generate an island detecting disturbance signal; and if the mains current of the utility power source is less than the preset error value, the current-controlled power converter generates an island Detecting the disturbance signal, and re-detecting the mains current and taking the absolute value thereof. If the absolute value is still less than the preset error value, it is determined that the islanding operation phenomenon occurs, and the mains power supply and the distributed power generation system are Untie.

Another object of the present invention is to provide an islanding operation detecting method for a mains parallel current-controlled electric energy converter, which is applied to a power system having a mains power supply, a distributed power generation system and a load, the mains power supply Connecting the load via a first electromagnetic switch, the distributed power generation system is connected to the load via a second electromagnetic switch, the method comprising: a. detecting a mains current; b. determining an absolute value of the mains current, determining Whether the absolute value is greater than a predetermined error value; c. if the absolute value is greater than the preset error value, setting an island detecting disturbance signal to zero, and controlling the first electromagnetic switch and the second electromagnetic switch Closing, connecting the mains power supply and the distributed power generation system to the load, and returning to the foregoing step a; d. if the absolute value is less than the preset error value, the island detection disturbance signal is set to be non-zero, and again Detecting the mains current; e. taking an absolute value of the re-detected mains current, determining whether the absolute value is greater than the preset error value; f. if the absolute value is greater than the preset error value, performing the foregoing steps c; g. If the absolute value is less than the preset error value, it is determined that an islanding operation occurs, and the first electromagnetic switch and the second electromagnetic switch are controlled to open, so that the mains power supply and dispersion The power generation system is disconnected from the load.

According to the foregoing technical means, when the power supply of the mains power supply is normal and the power generated by the distributed power generation system and the total power consumed by the load are not balanced, the current control type power converter does not add an island detecting disturbance signal. To maintain good power quality, maintain a low total harmonic distortion rate. In fact, the power generated by the distributed power generation system and the total energy consumed by the load reach a power balance, and the chance of occurrence is extremely small, and the occurrence time is very short. Therefore, the island operation detection method proposed by the present invention can accurately detect the island. It does not need to continuously disturb the output current of the current-controlled power converter, so the time and number of disturbances of the distributed power generation system can be greatly reduced to maintain good power quality.

Furthermore, when the mains power supply is abnormal, the current-controlled electric energy converter is disturbed by the output current, and it is also possible to effectively determine whether or not the islanding operation occurs.

Referring to the first figure, the present invention can be applied to the power system architecture. The power system mainly includes a mains power supply (10), a distributed power generation system (20), a load (30), and a first electromagnetic The switch (40) and a second electromagnetic switch (50), wherein the distributed power generation system (20) is composed of a direct current power (21) and a current controlled power converter (22), and the commercial power supply (10) Providing a mains power supply voltage (11) and a mains current (12), the mains supply (10) being connected to the load (30) via the first electromagnetic switch (40), the distributed power generation system (20) Connected to the load (30) via the second electromagnetic switch (50).

The technical features of the islanding operation detection method proposed by the present invention are different from other active detection island operation methods except that the islanding operation is effectively detected, that is, when the commercial power source (10) is normal and has energy in and out of the city power source (10) When the distributed power generation system (20) does not disturb the power system, the overall power quality can be improved; conversely, the islanding detection technique of the present invention is only when the mains power supply (10) is powered off or when the distributed power generation system ( 20) When the generated electric energy happens to be equal to the energy consumed by the load (30), the output current of the current-controlled power converter (22) is added to an island detecting disturbance signal ΔI to determine whether or not islanding operation occurs. The basic principle The description is as follows: First, referring to the second figure, the islanding operation detection method of the distributed power generation system of the present invention is implemented by the current control type power converter (22), the current control type power converter (22) It is a current-controlled DC/AC power converter that not only has the function of active power filter, but also has the function of energy return, so whether the load (30) is non- For linear load or any load, the mains current (12) will be controlled to a pure sine wave current with the same phase or phase as the mains supply voltage (11) (180 degrees difference), assuming the mains supply voltage (11) It can be expressed by the following formula as v _s ( t )= V _s sin( ωt ) (1)

The nonlinear load current can be expressed as

After the current-controlled power converter (22) generates a compensation current for compensation, the mains current (12) can be expressed as i _s ( t )=± I _{s 1} sin( ωt ) (3)

In the formula (3), + I _{s 1 is} defined as the mains current (12) is in phase with the mains supply voltage (11), and the actual power flow flows from the mains supply (10) into the load (30); I _{s 1 is} defined as the opposite of the mains current (12) and the mains supply voltage (11) (180 degrees difference), and the actual power flow flows from the distributed power generation system (20) to the mains supply (10).

Therefore, the reference signal of the compensation current generated by the current-controlled power converter (22) can be calculated as i _con ( t )= i _L ( t )- i _s ( t ) (4)

If the output current of the current-controlled power converter (22) is i _con ( t ), the mains current (12) will be a sinusoidal current, and the phase of the mains current (12) will be in phase with the mains supply voltage (11) or The phases are opposite (180 degrees difference).

The active power filter is mainly used under any load, such as non-linear load. The mains current (12) can effectively control and maintain a pure sine wave current and is in phase or opposite to the mains supply voltage (11). A difference of 180 degrees). The current controlled power converter (22) controls the power balance concept so that the magnitude of the mains current (12) is dependent on the mains power supply (10), the distributed power generation system (20) and the load (30) in the system. The power balance.

In a voltage source type current controlled power converter, a DC bus is placed on the DC bus of the current controlled power converter (22) as an energy storage and buffer to adjust the DC bus voltage (23). In the steady state of the system, the actual power supply provided by the mains power supply (10), the actual power generated by the distributed power generation system (20) and the actual power consumed by the load (30) will be balanced, so The average value of the DC bus voltage (23) will reach a stable constant value. If the system power is not balanced due to the instantaneous change of the load (30), the DC capacitor must provide the difference between the mains power supply (10) and the load (30). Therefore, the current-controlled power converter (22) must adjust the DC. DC bus voltage on the capacitor (23). If the actual power generated by the mains power supply (10) and the direct current power (21) is less than the actual power consumed by the load (30), the DC bus voltage (23) will decrease. At this time, the mains current (12) The value of the control command will increase, that is, to increase the mains current (12), so that the actual amount of power provided by the mains supply (10) increases to achieve power balance. Conversely, if the actual power generated by the mains power supply (10) and the direct current power (21) is greater than the actual power consumed by the load (30) due to the instantaneous change of the load (30), the system power cannot be balanced, and the DC bus voltage (23) ) will rise, at this time, the control command value of the mains current (12) will be reduced, that is, to reduce the mains current (12), reduce the real power supply (10) provided Power balance to achieve power. Therefore, adjusting the DC bus voltage (23) can control the magnitude of the mains current (12) and achieve the power balance of the overall system.

The control mode of the current-controlled power converter (22) needs to detect three feedback signals, which are a mains power supply voltage signal, a constant current bus voltage signal and a mains current signal. The mains supply voltage (11) detects its voltage signal via a first voltage detector (605) and inputs it to a waveform generator (606) which generates a same voltage as the mains supply voltage (11). The sinusoidal reference signal with the same frequency and the adjusted DC bus voltage (23) are mainly used to provide the power balance between the mains power supply (10), the distributed power generation system (20) and the load (30). The DC bus voltage (23) is detected by a second voltage detector (600), and is input to a subtractor (601) together with the DC set voltage to generate a DC voltage error signal. The voltage error signal is input to a proportional integral controller (602) to generate a mains current amplitude control signal that is a DC bus voltage necessary for the current controlled power converter (22) in consideration of steady state ( 23) The size is determined. The mains current amplitude control signal is input to an adder (604) and the island detecting disturbance signal ΔI is added to generate a reference signal of the mains current amplitude, and the main current amplitude reference signal is used to control the main current (12). The amplitude, the islanding operation detecting method of the distributed power generation system proposed by the present invention is as shown in the third figure, which generates an island detecting disturbance signal ΔI, and the disturbance signal is injected into the island detecting shown in the second figure. Disturbing signal △I, if the absolute value of the mains current is greater than the preset error value, the island detecting disturbance signal ΔI is zero; conversely, if the absolute value of the mains current is less than the preset error value, the island detecting disturbance signal is ΔI will not be equal to zero.

The output of the waveform generator (606) and the reference mains current amplitude signal system The input multiplier (607) is multiplied to obtain a mains current reference signal whose phase is in phase or phase opposite to the mains supply voltage (180 degrees difference).

After the mains current (12) obtains the current signal via a current detector (608), the mains current reference signal is input to a subtractor (609) to obtain a mains current error signal. The mains current error signal is sent to an error amplifier (610), and the output signal of the error amplifier (610) is transmitted to a driving circuit (611), and then a driving signal is generated by a driving circuit (611) to drive current control. Power electronic switch of the electric energy converter (22).

Please refer to the third figure, which is a flow chart of the island operation detection method of the present invention. The main steps are as follows: detecting the mains current (701); determining whether the absolute value of the main current (12) is greater than a preset error value. I _err (702); if the absolute value of the detected mains current (12) is greater than a preset error value I _err , the island detecting disturbance signal ΔI is set to zero, and the first and second electromagnetic switches ( 40) (50) closing, so that the mains power supply (10) and the distributed power generation system (20) are connected to the load (30) (706), and the current-controlled power converter (22) does not generate current disturbance and continues to operate; If the absolute value of the detected mains current (12) is less than the preset error value I _err , the island detecting disturbance signal ΔI is not equal to zero (703), and the preset error value I _err is to avoid the measurement. The error is very small but not equal to zero; therefore, the island detection disturbance signal ΔI is added to the control of the current-controlled power converter (22), and the utility current (12) is again detected (704); the utility current is determined. if (12) the absolute value of the error is greater than a preset value I _err (705); Detected by the mains current (12) of an absolute value greater than the error set in advance the value I _err, it represents the current mains supply (10) normal, but distributed power generation system (20) generated by the electric power happens to the load (30) The total energy consumed is equal. Therefore, the island detecting disturbance signal ΔI is set to zero, the first and second electromagnetic switches (40) (50) are closed (706), and the current-controlled power converter (22) is not Current disturbance is generated and continues to operate; conversely, when the absolute value of the commercial current (12) detected by adding the disturbance signal ΔI is not smaller than the preset error value I _err , the detection is detected. The distributed power generation system (20) is in an island operation, so the first and second electromagnetic switches (40) (50) are opened (707), and the distributed power generation system (20) is cut off from the commercial power supply (10), and Cut off the load (30) and stop the system.

The islanding operation detecting method proposed by the invention adds a current amplitude disturbance amount ΔI not equal to zero when the main current (12) is almost equal to zero to destroy the overall system power balance, if the main current (12) is still almost equal to zero, The island operation can be detected. This also means that after the mains current (12) is added to the amplitude disturbance amount ΔI which is not equal to zero to destroy the real power balance, there is still no mains current (12) flowing on the mains power supply (10) side. Therefore, the island detecting method proposed by the present invention can effectively detect the islanding operation under the most difficult detection condition.

The general active island operation detection method uses a disturbance signal to continuously input the output current of the commercial parallel power converter, and compares the traditional active island operation detection method. The advantage of the island operation detection method proposed by the present invention is that the utility power source (the utility power source ( 10) Normal power supply, and generated by the distributed power generation system (20) When the total energy consumed by the power and load (30) is not balanced, the current-controlled power converter (22) does not add a disturbance signal, so that the mains current waveform can reach an approximate sine wave and the mains voltage (11) The same phase or phase is opposite (180 degrees difference), so the mains current (12) can always maintain a low total harmonic distortion rate, and in practical applications, the total power consumption and load (30) generated by the distributed power generation system (20) The opportunity for the power to reach the power balance is very small, and the time of occurrence is very short. Therefore, the islanding operation detection method proposed by the invention can not only accurately detect the island operation, and does not need to continuously perturb the current-controlled power converter (22). The output current will greatly reduce the time and frequency of disturbing the distributed power generation system (20).

The above are only the preferred embodiments of the present invention and are not intended to limit the scope of the invention. That is, the scope of the patent application of the present invention is modified by those skilled in the art and is intended to be protected by the scope of the patent application, and is covered by the scope of the invention.

(10) ‧‧‧mains power supply

(11) ‧‧‧mains supply voltage

(12) ‧‧‧City current

(20)‧‧‧Distributed power generation system

(21)‧‧‧DC power

(22)‧‧‧ Current Controlled Energy Converter

(23)‧‧‧DC bus voltage

(30)‧‧‧ Load

(40)‧‧‧First electromagnetic switch

(50)‧‧‧Second electromagnetic switch

(600)‧‧‧Second voltage detector

(601)‧‧‧Subtractor

(602) ‧‧‧Proportional Integral Controller

(604)‧‧‧Adder

(605)‧‧‧First voltage detector

(606)‧‧‧ Waveform Generator

(607)‧‧‧Multiplier

(608)‧‧‧ Current Detector

(609)‧‧‧Subtractor

(610)‧‧‧Error amplifier

(611)‧‧‧ drive circuit

First: The architecture diagram of the mains power system and the distributed power generation system of the present invention.

Second: A control block diagram of a current controlled power converter incorporating the islanding operation detection method of the distributed power generation system of the present invention.

The third figure: a flow chart of the island running detection method of the present invention.

Claims (6)

An island running detection method for a mains-connected current-controlled power converter includes: connecting a distributed power generation system to a mains power supply and supplying power to a load, wherein the distributed power generation system includes a DC power supply and a current-controlled power converter, which provides a real power to the mains power supply; the mains current of the mains power source is taken as an absolute value, and if the absolute value is greater than a predetermined error value, the mains power supply is determined to be normal, An island detecting disturbance signal is set to zero, and the current control type power converter output current does not generate an island detecting disturbance; and if the mains current of the utility power source has an absolute value smaller than the preset error value, an island detecting is performed The disturbance signal is not equal to zero. The current-controlled power converter output current generates an island detection disturbance, and then re-detects the utility current and takes its absolute value. If the absolute value is still less than the preset error value, it is determined. In order to cause islanding, the mains power supply and the distributed power generation system are uncoupled. The island running detection method of the commercial power-coupled current-controlled power converter according to the first aspect of the patent application, wherein the output current ( i _con ( t )) of the current-controlled power converter is based on a reference signal Decide. The islanding operation detecting method of the utility model as described in claim 2, wherein the reference signal is a real power control signal. For example, in the islanding operation detection method of the commercial power-coupled current-controlled power converter according to Item 3 of the patent application scope, the actual power control signal is the same frequency and the same phase or phase opposite to the utility power source (the difference is 180 degrees). The sinusoidal signal. For example, in the islanding operation detection method of the commercial power-coupled current-controlled power converter according to the first aspect of the patent application, when the mains power supply is determined to be normal, the current-controlled power converter generates a compensation current to make the utility power The current of the power supply is a sinusoidal current that is in phase or phase opposite to the voltage of the mains supply (180 degrees out of phase). An island running detection method for a mains-connected current-controlled power converter is applied to a power system having a mains power supply, a distributed power generation system and a load, wherein the mains power supply is connected via a first electromagnetic switch The load, the distributed power generation system is connected to the load via a second electromagnetic switch, the method comprising: a. detecting a mains current; b. taking an absolute value of the mains current, determining whether the absolute value is greater than a predetermined value An error value; c. if the absolute value is greater than the preset error value, setting an island detecting disturbance signal to zero, and controlling the first electromagnetic switch and the second electromagnetic switch to close, so that the main power source and the distributed power generation The system is connected to the load and returns to the foregoing step a; d. if the absolute value is less than the preset error value, the island detection disturbance signal is set to be non-zero, and the utility current is again detected; e. Re-detecting the mains current as an absolute value, determining whether the absolute value is greater than the preset error value; f. if the absolute value is greater than the preset error value, performing Step c; g. If the absolute value is less than the preset error value, it is determined that an islanding operation occurs, and the first electromagnetic switch and the second electromagnetic switch are controlled to be turned on, so that the mains power supply and the distributed power generation system and the load are Broken off.