JPH07337088A - Inverter - Google Patents

Abstract

PURPOSE:To obtain an inverter which can be operated with highest efficiency by controlling the AC output voltage such that the input voltage is minimized. CONSTITUTION:A current sensor 3 detects the input current to a rectifier 1 from an AC power supply 10. A zero-cross detector 4 detects the zero-cross of input voltage from the AC power supply 10. Based on a zero-cross signal from the zero-cross detector 4, a sine wave generating section 22 generates a sine wave having a period identical to that of AC voltage from the AC power supply 10. Based on an input current signal from the current sensor 3 and a sinusoidal signal from the sine wave generating section 22, a power operating section 23 operates a value approximately proportional to the power being fed from the AC power supply 10 to the rectifier 1. A control section 24 then controls the AC output voltage from the inverter section 2 such that the value substantially proportional to the power operated at the power operating section 23 is minimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter which controls an induction motor with high efficiency without being affected by changes in operating frequency and load.

[0002]

2. Description of the Related Art Conventionally, as an inverter for driving an induction motor, as shown in FIG. 6, a rectifier 61 connected to an AC power source 70 and an inverter section 62 connected to a DC voltage output terminal of the rectifier 61. A current sensor 63 provided between the AC voltage output terminal of the AC power supply 70 and the AC voltage input terminal of the rectifier 61, and a zero-cross detector 64 connected to both AC voltage input terminals of the rectifier 61. There is something. Further, a smoothing capacitor 71 provided between both DC voltage output terminals of the rectifier 61, a reactor 72 provided between one end of the smoothing capacitor 71 and one output terminal of the rectifier 61, and the smoothing capacitor 71. And an shunt resistor 73 for detecting an overcurrent provided between the other end of the inverter and the inverter unit 62. The induction motor 67 is connected to the AC voltage output terminal of the inverter unit 62.

The inverter configured as described above controls the AC voltage output of the inverter section 62 so that the signal representing the input current from the current sensor 63 is minimized so that the induction motor 67 can be operated with high efficiency. (Japanese Patent Laid-Open No. 6-1
No. 1217).

[0004]

In the above inverter, the AC voltage output of the inverter section 62 is controlled so that the input current from the current sensor 63 is minimized.
Since it does not minimize the input power, the induction motor 6
There is a problem that 7 cannot be operated at maximum efficiency.

Further, an average value rectification circuit for averaging the signal representing the input current from the current sensor 63 is required, and the AC output voltage of the inverter unit 62 is calculated in consideration of the time constant of the average value rectification circuit. It has the disadvantage of having to be controlled.

Therefore, an object of the present invention is to provide an average value rectification circuit or the like for controlling the AC voltage output of the inverter so that the input power is minimized to achieve maximum efficiency operation and for averaging the signal from the current sensor. It is to provide an inverter that can be omitted.

[0007]

In order to achieve the above object, the inverter of claim 1 has a rectifier connected to an AC power source and an input terminal connected to a DC voltage output terminal of the rectifier, and an AC voltage output terminal. In an inverter equipped with an inverter unit connected to an induction motor, a power detection unit that detects a value corresponding to the power input to the rectifier from the AC power supply, and the power detected by the power detection unit. And a control means for controlling the AC output voltage of the inverter unit so that the corresponding value becomes a minimum.

The inverter of claim 2 is the same as that of claim 1.
In the inverter, the power detection means is an input current detection means for detecting an input current flowing from the AC power supply to the rectifier, a zero-cross detection means for detecting a zero-cross point of an AC voltage from the AC power supply, and the zero-cross detection. Based on the signal from the means representing the zero crossing point,
Based on a sine wave generating means for generating a sine wave having the same cycle as the AC voltage from the AC power source, a signal representing the input current from the input current detecting means and a signal representing the sine wave from the sine wave generating means. And an electric power calculation means for calculating a value corresponding to the electric power input from the AC power supply to the rectifier.

[0009]

According to the inverter of the first aspect, the power detection means detects a value corresponding to the power input from the AC power supply to the rectifier, and the control means includes:
The AC output voltage of the inverter section is controlled so that the value corresponding to the electric power detected by the electric power detection means becomes a minimum.

Therefore, the induction motor connected to the AC voltage output terminal of the inverter section can be operated with maximum efficiency.

According to the inverter of claim 2, in the inverter of claim 1, the power detecting means includes an input current detecting means, a zero-cross detecting means, a sine wave generating means and a power calculating means, The wave generating means generates a signal representing a sine wave having the same period as the AC voltage from the AC power supply, based on the signal representing the zero cross point from the zero cross detecting means. Then, based on the signal representing the input current from the input current detecting means and the signal representing the sine wave from the sine wave generating means, the power calculating means corresponds to the power input to the rectifier from the AC power supply. Calculate the value. Then, the control means is
The AC output voltage of the inverter unit is controlled so that the value corresponding to the electric power calculated by the electric power calculating means becomes a minimum.

Therefore, when the inverter of the present invention is used in an air conditioner, for example, based on the zero-cross point from the zero-cross detection means already provided for transmission,
Since the sine wave generating means can generate a signal representing a sine wave instead of the input voltage, a signal representing the sine wave is detected without detecting the input voltage from the AC power supply using a new voltage sensor. A value corresponding to the electric power input to the rectifier can be easily obtained by using the signal representing the input current from the current detecting means. Further, by obtaining the electric power of the signal representing the input current from the input current detecting means as an instantaneous value, the average value rectifying circuit for averaging the signal representing the input current from the input current detecting means can be omitted. Further, by omitting the average value rectifying circuit, it becomes unnecessary to consider the time constant of the average value rectifying circuit when the control means controls the AC output voltage of the inverter section.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The inverter of the present invention will be described in detail below with reference to an embodiment.

FIG. 1 is a block diagram of an inverter according to an embodiment of the present invention. Reference numeral 1 is a rectifier composed of a diode bridge in which an AC voltage output terminal of an AC power source 10 is connected to an AC voltage input terminal, and 2 is the above-mentioned. The inverter section 3 whose input terminal is connected to the DC voltage output terminal of the rectifier 1 is an input current detector provided between one end of the AC voltage output terminal of the AC power supply 10 and one end of the AC voltage input terminal of the rectifier 1. A current sensor as a means, 4 is a zero-cross detector as a zero-cross detecting means connected between both AC voltage input terminals of the rectifier 1, and 5 is an input current signal from the current sensor 3 and the zero-cross detector 4 A microcomputer (hereinafter, referred to as a microcomputer) that outputs a PWM (pulse width modulation) signal in response to a zero-cross signal representing the zero-cross point of A drive circuit that receives a PWM signal from the microcomputer 5 and outputs a commutation control signal to the inverter unit 2 is an induction motor connected to an AC voltage output terminal of the inverter unit 2. In addition, the rectifier 1
A smoothing capacitor 11 is connected between the two DC voltage output terminals, and a reactor 12 is connected between one end of the smoothing capacitor 11 and one end of the DC voltage output terminal of the rectifier 1. In addition, an overcurrent detection shunt for detecting an overcurrent flowing from the DC voltage output terminal of the rectifier 1 to the input terminal of the inverter unit 2 between the other end of the smoothing capacitor 11 and one end of the input terminal of the inverter unit 2. The resistor 13 is connected.

The microcomputer 5 receives an input current signal from the current sensor 3 (shown in FIG. 2 (b)) and A / D converts the input current signal, and the zero-cross detector. Zero cross signal from 4 (shown in Figure 2 (a))
In response to this, a sine wave generator 22 as sine wave generating means for generating a sine wave pseudo voltage signal (shown in FIG. 2 (c)), and an A / D converted input from the A / D converter 21. A power calculation unit 23 as a power calculation unit that calculates a value that is substantially proportional to the power based on the signal representing the instantaneous value of the current signal and the sine wave pseudo voltage signal from the sine wave generation unit 22;
A control unit 24 as a control unit that outputs a PWM signal based on a value that is substantially proportional to the power from the power calculation unit 23 is provided. The current sensor 3, the zero-cross detector 4, the A / D converter 21, the sine wave generator 22, and the power calculator 23 constitute power detection means.

The zero-cross detector 4 has an AC power source 10
The zero-cross point of the input voltage input to the rectifier 1 is detected, and the zero-cross signal shown in FIG.
Then, based on the zero-cross signal, the sine wave generator 22 of the microcomputer 5 uses the sine wave data stored in the table in advance to generate the pseudo voltage signal shown in FIG. The pseudo voltage signal may be calculated by using a predetermined calculation formula. Then, the current sensor 3
2B detects the input current shown in FIG. 2B and outputs an input current signal representing the input current, and the A / D converter 21 A / D converts the input current signal to obtain the input current. A signal representing the instantaneous value of is output. The above microcomputer 5
The power calculator 23 calculates the power input to the rectifier 1 based on the pseudo voltage signal and the signal representing the instantaneous value of the input current. That is, assuming that the instantaneous voltage of the pseudo voltage signal is v and the instantaneous value of the input current corresponding to the instantaneous voltage is i, the power P is P = 1 / T (∫v · idt) (T: pseudo voltage signal One cycle time). The electric power P thus obtained has a value corresponding to the electric power actually input to the rectifier 1, that is, a value substantially proportional to the electric power. That is, since the voltage input to the rectifier 1 is stable, it can be considered that the pseudo voltage signal is substantially proportional to the actual input voltage. Therefore, by minimizing the value that is substantially proportional to the electric power, the electric power actually input from the AC power supply 10 to the rectifier 1 can be minimized.

FIG. 3 is a flow chart showing the operation of the control section 24 of the microcomputer 5. The control section 24 carries out the processing of control 1 for increasing or decreasing the output voltage of the inverter section 2 according to the change of the input current, and the operating frequency. When the value is changed, the process of control 2 for increasing or decreasing the output voltage of the inverter unit 2 according to the operating frequency is performed. It should be noted that this process is repeatedly performed at predetermined intervals.

The processing of the control unit 24 will be described below with reference to the flowchart of FIG.

First, in step S1, it is determined whether or not the operating frequency matches the command frequency. If it is determined that the operating frequency matches the command frequency, the process proceeds to step S2.
Next, in step S2, it is determined whether or not a predetermined t _w seconds have elapsed after the operating frequency matches the command frequency,
When t _w seconds have elapsed, the process proceeds to step S3. On the other hand, t _w
If the second has not elapsed, the processing is terminated, and steps S1 and S2 are repeated until _tw seconds have elapsed. That is,
After changing the operating frequency, it waits for the motor current and the like to reach a stable state. Then, in step S3, it is determined whether or not the control 1 is the first time. If the control 1 is the first time, the process proceeds to step S4, and the voltage correction width ΔV = c · f _out + d (c, d: constant,
f _out : operating frequency) is calculated. Then, in step S5, the voltage correction width ΔV is subtracted from the reference output voltage V ₀ at the maximum efficiency point at the operating frequency f _out Hz under the standard load condition −
After correction, the process proceeds to step S11. That is, the output voltage V ₁ = V ₀ −ΔV is calculated, and the first time of the process of the control 1 is the inverter unit 2
The PWM signal is output from the control unit 24 so that the output voltage of V ₁ becomes V ₁ . The reference output voltage V _{0 at} the maximum efficiency point at the operating frequency f _out Hz under the standard load condition
Is calculated by the reference output voltage V ₀ = a · f _out + b (a, b: constant).

On the other hand, when it is not the first time of the control 1 in step S3, the process proceeds to step S6, and a change in power is determined. That is, it is determined that the power has increased when the value that is substantially proportional to the power is increased based on the signal that is calculated by the power calculation unit 23 and that is substantially proportional to the power. It is determined that the power has decreased when the value to be reduced becomes smaller, and it is determined that the power has not changed when the value substantially proportional to the power does not change. And
If it is determined in step S6 that the power has decreased, the process proceeds to step S7, where the ± polarity that determines the direction of increase (+) or decrease (-) of the output voltage is maintained, while if it is determined that the power has increased, the step Proceeding to S8, the ± polarities are inverted. That is, when the output voltage of the inverter unit 2 is in the increasing (+) direction, it is changed to the decreasing (-) direction, while when the output voltage of the inverter unit 2 is in the decreasing (-) direction, it is increased (-). +)
Make it the direction. If the power does not change in step S6, the process ends, and the process is repeated from step S1.

Next, in step S9, control 1 is performed based on the ± polarity determined in step S7 or step S8.
Process. That is, V _{n + 1} = V _n ± ΔV (V _n : previous output voltage, V _{n + 1} :
The current output voltage) is calculated, and the PWM signal is output from the control unit 24 so that the output voltage of the inverter unit 2 becomes V _{n + 1} . Therefore, in the first step of the processing of control 1 after the operating frequency matches the command frequency in step S1, the output voltage is determined to have a negative polarity in the negative (-) direction, and it is determined that the power has increased ± polarity. The output voltage is gradually decreased from the reference output voltage V ₀ until the output voltage is inverted. And step S
In step 10, voltage correction limit processing is performed. That is, the output voltage V _{n + 1} corrected in step S9 is the stop line (see FIG. 5).
It is determined whether or not the output voltage V _{n + 1} exceeds the output voltage V _{n + 1} when the output voltage V _{n + 1} exceeds the output voltage V _{n + 1} .

Next, in step S11, the control voltage rate K = V _{n + 1} / V ₀ is calculated, and this processing is ended. The initial value of the control voltage ratio K is 1.

If it is determined in step S1 that the operating frequency does not match the command frequency, the process proceeds to step S12, control 2 is performed, and V _m = K (af _out + b) (a, b: A constant) is calculated, and the voltage command signal is output from the control unit 24 so that the output voltage of the inverter unit 2 becomes V _m . That is, while gradually changing the operating frequency to the command frequency, the output voltage V _m corrected by the control voltage ratio K from the output voltage V ₀ at each operating frequency at that time is output from the inverter unit 2.

Therefore, if the command frequency is changed and the operating frequency fluctuates, the control 2 of step S12
The process controls the output voltage and the operating frequency is coincident with the command frequency, shifts to the processing control 1 after waiting t _w seconds, increase or decrease the output voltage, the power is to operate at maximum efficiency point of minimum .

For example, as shown in FIG. 4, the relationship between the output voltage and the electric power of the inverter section 2 when the operating frequency is constant is represented by a U-shaped characteristic curve. Then, when the operating frequency is a predetermined frequency, the output voltage V _{0 at the} operating frequency f _out Hz under the standard load condition is reduced by ΔV with a negative polarity to reduce the output voltage by ΔV, and when the output voltage is V ₁ , the power is small. Become. Further, if the output voltage is decreased by ΔV in the negative polarity to become the output voltage V ₂ , the power gradually decreases. Then, when the output voltage is reduced by ΔV from the output voltage V ₂ by ΔV to the output voltage V ₃ , the power gradually increases beyond the minimum value. At this time, the polarity is inverted and the output voltage is increased by ΔV in + polarity to increase the output voltage V
Return to ₄ . In this way, the output voltage of the inverter section 2 is controlled so that the maximum efficiency point, that is, the electric power is minimized by repeatedly increasing and decreasing the output voltage of the inverter section 2.

Further, as shown in FIG. 5, when the command frequency is changed from the processing state of the control 1 for variably controlling the output voltage, the control state shifts to the processing state of the control 2 and a command is _given from the output voltage V _{n at the} maximum efficiency point. The output voltage of the inverter unit 2 is lowered up to the specified frequency in accordance with the output voltage characteristic with respect to the operating frequency under the standard load condition (shown in the V / F characteristic when the frequency changes in FIG. 5). Then, after the operation frequency coincides with the command frequency, the process of control 1 for varying the output voltage is performed after _tw seconds have elapsed. The upper and lower limits of the variable range of the output voltage of the inverter unit 2 are the voltage correction limits (stop line) shown by the dotted line in FIG.

As described above, based on the pseudo voltage signal calculated based on the zero-cross signal from the zero-cross detector 4 by the sine-wave generator 22 and the input current signal from the current sensor 3, the power calculator 23 is , A value that is approximately proportional to the electric power that is input from the AC power supply 10 to the rectifier 1 is calculated, and the control unit 24 controls the PWM signal so that the value that is approximately proportional to the electric power is minimized. Change the AC output voltage. Therefore, the induction motor 7 can be controlled with maximum efficiency. Further, by minimizing the electric power input to the rectifier 1 from the AC power source 10, the rectifier 1, the smoothing capacitor 11, the reactor 12, the power module of the inverter unit 2 and the loss of the induction motor 7 are taken into consideration as a whole inverter. The efficiency can be improved. In addition, if an additional circuit (for example, an active filter or a solar cell) is added between the AC power supply 10 and the inverter unit 2, the loss of the additional circuit can be expected, and the circuit type of the inverter such as a current type inverter can be expected. Even if is changed, the same effect can be obtained.

Further, for example, when this inverter is used in an air conditioner, the sine wave generator 2 is based on the zero cross point from the zero cross detector 4 provided for transmission.
2 can generate a sinusoidal pseudo voltage signal instead of the input voltage from the AC power supply 10, so that it is not necessary to detect the input voltage from the AC power supply 10 using a new voltage sensor, and Wave pseudo voltage signal and current sensor 3
A value substantially proportional to the electric power input to the rectifier 1 can be easily obtained by using the input current signal from. Also,
Since an instantaneous value of the input current signal from the current sensor 3 is used to calculate a value that is substantially proportional to the electric power, an average value rectifying circuit or the like for averaging the input current signal can be omitted. Further, by omitting the average value rectifying circuit, it becomes unnecessary to control the output voltage of the inverter unit 2 in consideration of the time constant of the average value rectifying circuit.

In the above embodiment, the zero cross detector 4 is used.
Although the pseudo voltage signal is calculated on the basis of the signal indicating the zero cross point from the above, a voltage sensor for detecting the input voltage or the like may be provided. Further, the electric power input to the rectifier may be obtained from the input voltage signal from the voltage sensor and the input current signal from the input current detecting means.

Further, although the inverter section 2 controls the output voltage by the pulse width modulated PWM signal, the control method of the output voltage of the inverter section is not limited to this, and the pulse amplitude modulation method or the pulse frequency modulation method is also applicable. Of course, the method may be used.

[0031]

As is apparent from the above, the inverter according to the invention of claim 1 has a rectifier connected to an AC power supply, an input terminal connected to the DC voltage output terminal of the rectifier, and an AC voltage output terminal induced. In an inverter having an inverter unit connected to an electric motor, the power detection means detects a value corresponding to the power input from the AC power supply to the rectifier, and the control means corresponds to the power detected by the power detection means. The AC output voltage of the inverter unit is controlled so that the value to be minimized is minimized.

Therefore, according to the inverter of the first aspect of the present invention, the induction motor connected to the AC voltage output of the inverter section can be operated with maximum efficiency.

According to a second aspect of the present invention, in the inverter according to the first aspect, the input current detecting means of the power detecting means detects the input current flowing from the AC power source to the rectifier, and the power detecting means. The zero-crossing detecting means detects the zero-crossing point of the AC voltage from the AC power source, and based on the signal representing the zero-crossing point from the zero-crossing detecting means, the sine wave generating means of the power detecting means is Generates a sine wave of the same cycle as the AC voltage, and the power calculation means of the power detection means is based on the signal representing the input current from the input current detection means and the signal representing the sine wave from the sine wave generation means. , A value approximately proportional to the electric power input to the rectifier from the AC power supply is calculated, and the control means corresponds to the electric power calculated by the electric power calculation means. There is to control the AC output voltage of the inverter section so that the minimum.

Therefore, according to the inverter of the second aspect of the present invention, for example, when this inverter is used in an air conditioner, a sine wave is generated based on the zero cross point from the zero cross detecting means already provided for transmission. Since the means can generate a signal representing a sine wave instead of the input voltage, it is not necessary to detect the input voltage from the AC power source by using a new voltage sensor, and the signal representing the sine wave and the current detection can be obtained. The signal representing the input current from the means can be used to easily determine the value corresponding to the power input to the rectifier. Further, since the value corresponding to the electric power is obtained based on the signal representing the input current from the input current detecting means and the signal representing the sine wave from the sine wave generating means, the input current from the input current detecting means is represented. An average value rectification circuit for averaging the signals can be omitted. Further, by omitting the average value rectifying circuit, it is not necessary to control the inverter unit in consideration of the time constant of the average value rectifying circuit.

[Brief description of drawings]

FIG. 1 is a block diagram of an inverter using a current change detection device according to an embodiment of the present invention.

FIG. 2 is a diagram showing signals of respective parts of FIG.

FIG. 3 is a flowchart showing the operation of the microcomputer of the inverter.

FIG. 4 is a diagram showing the relationship between the output voltage and power of the inverter.

FIG. 5 is a diagram showing a relationship between an operating frequency and an output voltage when a command frequency is changed.

FIG. 6 is a block diagram of a conventional inverter.

[Explanation of symbols]

1,61 ... Rectifier, 2,62 ... Inverter section, 3,63 ...
Current sensor, 4,64 ... Zero cross detector, 5 ... Microcomputer, 6 ... Drive circuit, 7,67 ... Induction motor, 10,7
0 ... AC power supply, 11, 71 ... Smoothing capacitor, 12, 7
2 ... Reactor, 13,73 ... Shunt resistor for overcurrent detection.

Claims (2)

[Claims] 1. A rectifier (1) connected to an AC power source (10)
And an inverter section (2) having an input terminal connected to a DC voltage output terminal of the rectifier (1) and an AC voltage output terminal connected to an induction motor (7), the AC power supply (10 ) From the rectifier (1) to detect a value corresponding to the electric power, and the inverter section (2) so that the value corresponding to the electric power detected by the electric power detecting means becomes a minimum. And a control means (24) for controlling the AC output voltage of the inverter. 2. The inverter according to claim 1, wherein
The power detecting means is an input current detecting means for detecting an input current flowing from the AC power source (10) to the rectifier (1).
(3), zero-cross detection means (4) for detecting the zero-cross point of the AC voltage from the AC power supply (10), and the AC power supply based on the signal representing the zero-cross point from the zero-cross detection means (4). From the sine wave generating means (22), the sine wave generating means (22) for generating a sine wave having the same cycle as the AC voltage from (10), the signal representing the input current from the input current detecting means (3) and the sine wave generating means (22). And a power calculation means (23) for calculating a value corresponding to the power input to the rectifier (1) from the AC power supply (10) based on the signal representing the sine wave of Inverter.