JPH0463612B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling load sharing between engine generators when they are operated in parallel.

In recent years, portable engine generators used at construction sites, etc., often have multiple small or medium-sized generators and operate them in parallel as necessary, due to the large changes in power consumption and transportation considerations. It's summery.

Engine generators are usually equipped with a governor with a so-called drooping characteristic, which lowers the number of revolutions as the load increases, so when the power load changes, the number of revolutions (frequency) changes accordingly. Since each engine has its own characteristics and it is difficult to make these drooping characteristics the same, the load factor of both generators is not equally shared during parallel operation. Therefore, a load sharing device is used in order to equalize this load factor and enable the use of both generators up to their total generator capacity.

The conventionally commonly used load sharing device and its method are explained with reference to FIGS. 1 and 2.
The figure is a block diagram of a load sharing device. The active power P shared by the engine generator is transmitted through current transformers CT ₁ and CT ₃ and transformers T ₁₁ and T ₁₃ from the generator bus through current and voltage signals. The obtained power is inputted to the active power detection circuit A to be determined, and outputted to the differential amplifier circuit B. Differential amplifier circuit B
Then, it is compared with the shared power signal of another generator (reference generator) supplied through the signal line S, and the result is applied to the determination circuit C. In the judgment circuit C, if the active power of the generator is larger than the value of the signal line S with an appropriate dead band width, the frequency lowering relay drive circuit RYa is turned on, and if it is smaller, the frequency raising relay drive circuit RYb is turned on. is turned on, and the shared power amount is controlled to be equal. Note that Ra and Rc are resistances.

The active power detection circuit A is shown in FIG. 2 and is composed of a current transformer CT ₁ , a transformer T ₁₁ , a diode bridge SR, an average value circuit D, etc.
The output voltage of CT ₁ is switched by the output of transformer T ₁₁ and the diode switching circuit SR, and the output is averaged by the average value circuit D to obtain the active power. In the case of three-phase power, this circuit is Use a set.
That is, voltage e and current i are set as e=√2
Esinωt, i=√2Isin(ωt+Θ), current transformer
The voltage ei generated across the resistor Rd connected across CT ₁ is given by the following equation.

ei=α・i・Rd sin(ωt+Θ) where α is the CT ratio This voltage ei is connected to the high resistance Re and the diode bridge.
When passed through a diode switch circuit composed of SR and transformer _T11 , when ev>0, ep=ei, and ev<0
Since ep=0 when

p=1/2π{∫〓〓〓 _t =〓 ₀ √2・α・I・R
₁ sin(ωt+Θ)dωt}=π/2α·I·Rd cosΘ On the other hand, since the power P of the AC circuit is expressed by EIcosΘ, the voltage ep is a value proportional to the power P, and the power is measured.

The load sharing method in the conventional load sharing device having the configuration described above relies on the configuration of resistors, capacitors, transistors, etc.
It is easily affected by ambient humidity, temperature, and power supply voltage noise, and because it is an analog process, the response is slow and control accuracy is poor, and it is practically impossible to measure power when the power factor drops. be. In addition, not only can it be used unless the two generators that share the load are almost the same, but the circuit is complex and maintenance and inspection is time-consuming, so improvements are desired from both reliability and economical points of view. There is.

The present invention has been developed in view of the above points, and aims to provide a simple configuration, high accuracy, and highly reliable load sharing method for engine generators. The voltage and current signals of the generator to be controlled are input to a microcomputer via zero cross and buffer circuits, while both signals are converted to DC digital signals via a level adjuster, filter and A/D converter. The phase angle of the voltage and current is calculated by counting the time between the points when the output changes at zero crossing using the clock of an oscillation circuit using a crystal oscillator, and then calculating the phase angle of the voltage and current. The active power of the generator is calculated from the voltage and current of the generator, and this is compared with the reference active power of the generator to command and control the frequency lowering relay or frequency increasing relay.

Hereinafter, one embodiment of the present invention will be described based on FIGS. 3 to 5.

FIG. 3 is a block diagram showing a load sharing device for an engine generator for explaining the method of the present invention.
ZC ₁ to ZC ₄ are zero crosses, BF ₁ to _{BF 4} are buffer circuits, AT ₁ to AT ₄ are level adjusters, F ₁ to F ₄ are filters, AD is an A/D converter (analog digital converter), and CPU is a micro computer,
CR is a crystal oscillator, IC ₅ to _{IC 6} are buffers, RY ₁ is a frequency lowering relay, and RY ₂ is a frequency increasing relay. Note that 1a is the terminal for the input voltage signal detected from the power line of the generator to be subjected to load sharing control, 2a is the terminal for the input current signal, 4a is the terminal for the input voltage signal detected from the power line of the reference generator, and 5a is the terminal for the input voltage signal detected from the power line of the generator to be controlled by load sharing. It is also a terminal for input current signals. zero cross here
ZC ₁ and zero cross ZC ₂ to ZC ₄ , buffer circuit BF ₁ and buffer circuit BF ₂ to _{BF 4} , level adjuster AT ₁ and level adjuster AT ₂ to _{AT 4} , filter F ₁ and filter
_F2 to _F4 are similar.

Zero cross ZC ₁ receives an input voltage signal from terminal 1a and changes the output when the signal passes through zero potential, and consists of an operational amplifier OP ₁ and a resistor.
Consists of R ₁ , R ₂ , diodes S ₁ , S ₂ ,
The negative input terminal of the operational amplifier _OP1 is connected to the input voltage signal from the terminal 1a, and the positive input terminal is connected to zero potential.

The output of operational amplifier OP ₁ is amplified by infinite times the sum of the voltages applied to each input terminal depending on the polarity of the input terminals, so operational amplifier OP ₁
At the output terminal of , an operation is obtained in which the output signal level is switched at the zero V potential where the input signal is switched.

The diodes S ₁ and S ₂ are used to prevent a voltage higher than a certain value (0.5 to 0.7V) from being applied to the operational amplifier OP ₁ , and the resistors R ₁ and R ₂ are used to control the current value flowing through the diodes S ₁ and S ₂ . Operational amplifier OP ₁ with limit
This is provided to improve the temperature characteristics of the

Buffer circuit BF ₁ connects the output signal of zero cross ZC ₁ to the microcomputer CPU.
It consists of a diode S ₃ that removes negative polarity output and a buffer IC ₁ that converts the output voltage signal (usually about 15V) of zero cross ZC ₁ to a signal of about +5V. Therefore, the output operation waveform of the buffer circuit _BF1 is as shown in FIG. 4c. Similarly, when the input voltage signal detected from the power supply line of the reference generator is received from the terminal 2a and passed through the buffer circuit _BF2 via the zero cross _ZC2 , the output operation waveform shown in FIG. 4d is obtained. Furthermore, S ₆ , S ₉ , S ₁₂
is a diode, and IC ₂ , IC ₃ , and IC ₄ are buffers.

The level adjuster AT ₁ receives the voltage signal from the terminal 1a and converts it into a DC signal that is easy to handle for the A/D converter AD _.
It consists of resistors _R11 to _R13 and a diode _S21 , and performs half-wave rectification and level conversion. That is, using operational amplifier OP ₁₁ as an inverting input amplifier,
Level conversion is performed by the ratio of input resistance R ₁₁ to feedback resistance R ₁₃ (conversion ratio = R ₁₃ /R ₁₁ ), and half-wave rectification is performed by diode S ₂₁ inserted in the output feedback circuit of operational amplifier OP ₁₁ . Note that the resistor _R12 is for stabilizing the operation of the operational amplifier _OP11 . The filter _F1 absorbs ripples contained in the input signal and outputs a signal containing only DC components. filter
The signal passed through _F1 is input to the A/D converter AD, converted to a digital signal, and sent to the microcomputer.
Output to CPU.

Similarly, the signal from terminal 2a is level adjusted.
AT ₂ , A/D converter AD through filter F ₂
The input analog signal is converted into a digital signal and output to the microcomputer CPU (this value is proportional to the effective value, as in the case of voltage). On the other hand, similarly to the above, a signal is received from the input voltage signal terminal 4a of the reference generator and output to the microcomputer CPU via the zero cross ZC ₃ and the buffer circuit BF _{3 .} F ₃ is output to the microcomputer CPU via the A/D converter AD.

Furthermore, the terminal 5a of the input current signal of the reference generator
It receives a signal from and outputs it to the microcomputer CPU via zero cross ZC ₄ and buffer circuit BF ₄ , and this signal is sent to level adjuster AT ₄ ,
The signal is output to the microcomputer via filter F ₄ and A/D converter AD. Here, the A/D converter AD is a so-called A/D converter with a multiplexer that switches the inputs of terminals 1a, 2a, 4a, and 5a and converts them into digital signals.
The arrow from the microcomputer CPU to the A/D converter AD indicates a multiplexer selection signal line.

The microcomputer CPU consists of an input/output device, an arithmetic device, a storage device, etc., and is equipped with an oscillation circuit clock using a crystal oscillator CR, and buffer circuits BF ₁ , BF ₂ , BF ₃ , BF ₄
It inputs the output signal from the A/D converter AD, measures the power of each of the two generators, compares the two, and if there is a difference, outputs it to buffer IC ₅ or buffer IC ₆ .

Power measurement is performed as follows.

That is, starting from the time when the output change (0→1 or 1→0) of the buffer circuit _BF1 shown in FIG. Counting is stopped when a change in direction occurs, and the resulting count T ₁ (FIG. 4c) is determined. Similarly, the time T ₂ (Fig. 4 d) from when the output of the buffer circuit BF ₁ changes in the same direction until the output of the buffer circuit BF ₂ changes in the same direction is determined, and the equation (1) is obtained. Calculate the phase angle Θ ₁ between voltage and current.

Θ ₁ = T ₂ / T ₁ × 360 (degrees) ...(1) Note that when the value calculated by equation (1) is 0 to 90°, it is slow phase, and when it is 90° to 270°, it is reverse power. When the angle is between 270° and 360°, it is phase advancing.

Next, the _Θ1 value obtained using equation (1) and the A/D converter AD
Calculate the active power P using equation (2) from the voltage E ₁ and current I ₁ obtained in .

P=K ₁・E ₁・I ₁・cosΘ ₁ ...(2) However, K ₁ is a constant of proportionality. Equation (2) is the active power in the case of a single phase, but in the case of three phases it is shown in Figure 5. In a circuit with a balanced three-phase load, using Eu-v ₁ as the voltage and Iv as the current, the active power P ₁ can be calculated using equation (3), taking into account the 30° difference between the line voltage and the phase current.

P ₁ = K ₁ · E ₁ · I ₁ cos (Θ ₁ −30) ...(3) On the other hand, the power P ₂ of the reference generator is similarly determined by the voltage and the output changes of the buffer circuits BF ₃ and BF ₄ . The phase angle Θ ₂ of the current is determined using equation (4) from the voltage E ₂ obtained by the A/D converter AD and the current I ₂ .

P ₂ = K ₂ · E ₂ · I ₂ cos (Θ ₂ −30) ...(4) K ₂ is a constant Next, compare the electric power P ₁ and P ₂ divided between the two generators calculated above, If the value of P ₂ - P ₁ is greater than the allowable value, it is amplified to relay control voltage via buffer IC ₅ , turns on frequency lowering relay RY ₁ , and drives the engine governor motor to reduce the engine speed. reduce

Also, if the value of P ₁ - P ₂ is greater than the allowable value, frequency increase relay RY ₂ is turned on via buffer IC ₆ . This controls the power shared by both generators to be the same. If the capacities of both generators are different, the shared power P ₁ and P ₂ are divided by their respective nominal capacities PS ₁ and PS ₂ and compared, and the load sharing ratio of both generators is controlled to be the same. Ru.

The load sharing method explained above is configured so that it can be used even when the _drooping characteristics _of the reference generator are _unknown . ₁ ,
BF ₂ , Level adjuster AT ₁ , AT ₂ , Filter F ₁ ,
F ₂ , A/D converter AD ₁ , microcomputer CPU ₁ and zero cross ZC ₃ , ZC ₄ that measures power P ₂ to another generator (reference generator);
Buffer circuit BF ₃ , BF ₄ , level adjuster AT ₃ ,
If you have AT ₄ , A/D converter AD ₂ , and microcomputer CPU ₂ and can measure the power of both generators digitally, the signals from buffer circuits BF ₃ , BF ₄ and A/D converter AD ₂ can be The power signal may be input to the computer CPU ₁ , or may be received from an output terminal 6a provided on the computer CPU as shown in FIG.

In addition, if each generator is equipped with a device that measures digitalized power as described above, the drooping characteristics of the speed governor as a standard can be set in advance in each microcomputer CPU, and compared with this. It is also possible to control the frequency up or down relay for each generator, or if the drooping characteristics of the standard generator can be measured in advance, this can be stored in the microcomputer CPU of the generator to be used for load sharing control. You can also do

As explained above, the automatic load sharing method for an engine generator according to the present invention processes the active power of the generator using a digital signal, so it is less affected by ambient conditions such as temperature and humidity, and is highly reliable. It is simple, requires no adjustment, and is easy to maintain.
Also, since the phase difference between the voltage and current of the generator is measured by the clock of the oscillation circuit using a crystal oscillator,
The accuracy is extremely high, the responsiveness is high, and the load sharing operation is quick. Furthermore, according to the embodiment shown in Fig. 3, it is possible to easily share the load even if the drooping characteristics of the partner generator are unknown, and not only the active power but also the reactive power and power factor can be easily determined. It has excellent effects such as highly accurate load sharing.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a load sharing device in a conventionally used portable engine generator.
FIG. 2 is a circuit diagram of power detection circuit A, FIG. 3 is a block diagram showing an automatic load sharing device for explaining the method of the present invention, and FIG. 4 is an explanatory diagram of operating waveforms in the method of the present invention. a and b are voltage signal waveforms obtained from both generators, c and d are output waveforms of buffer circuits BF ₁ and BF ₂ , and FIG. 5 is a balanced three-phase load vector diagram. 1a, 2a, 4a, 5a, 6a are terminals, ZC ₁ ~
ZC ₄ is zero cross, BF ₁ to _{BF 4} are buffer circuits,
AT ₁ to _{AT 4} are level adjusters, F ₁ to _{F 4} are filters,
AD is an A/D converter, CPU is a microcomputer, IC ₅ and IC ₆ are buffers, CR is a crystal oscillator,
RY ₁ is a frequency down relay and RY ₂ is a frequency up relay.

Claims (1)

[Claims] 1. Each of the voltage and current signals of the generator to be subjected to load sharing control is input to the microcomputer via a buffer circuit that changes the output when passing through zero potential to obtain a rectangular wave and removes the zero cross and negative polarity. Both signals are input to a microcomputer via a level adjuster and filter that converts them into DC signals at a level that can be easily handled by the A/D converter, and an A/D converter that converts them into digital signals, and the zero-cross signal output of the generator voltage is input to the microcomputer. The time from when a change occurs until the next change occurs is counted by the clock of an oscillation circuit using a crystal oscillator, and the generator current starts from the time when the zero-cross signal output of the generator voltage changes. Calculate the phase angle between voltage and current by counting the time until the same change occurs at the zero crossing of
The active power of the generator is calculated from this and the generator voltage and generator current obtained from the A/D converter, and this is compared with the reference active power of the generator to command and control the frequency lowering relay or frequency increasing relay. An automatic load sharing method for an engine generator, characterized in that the load is shared by the engine generator.