JPH06168791A - Inverter circuit - Google Patents

Abstract

PURPOSE:To simplify a circuit and improve a cost-performance ratio by changing a switching signal cycle with a microprocessor (MPU) for controlling an alternate current load. CONSTITUTION:An inverter circuit 20 is constituted of MPU 22 as a main component, and the digital output ports PD1 and PD2 thereof are connected to the gates G of 'n'-channel FETs 1 and 2. One of the electrodes of a fluorescent lamp 50 is also connected to a connection point between the source of FET 1 and the drain of FET 2. The gates G are thus exclusively applied with a switching signal, thereby feeding alternate power. Furthermore, the other electrode of the fluorescent lamp 50 is earthed via a resistor R3 and, at the same time, connected to an analog input port PA1. The quantity of state regarding an alternate current load is inputted to the MPU 22, and the switching cycle of a switching signal is changed by a stored program, thereby controlling a load. By the use of such a simplified circuit, a cost-performance ratio is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter circuit for converting DC power into AC power having a desired frequency to drive an AC load.

[0002]

2. Description of the Related Art Conventionally, various kinds of inverter circuits have been developed and are classified into self-excited or separately-excited inverter circuits and current-type or voltage-type inverter circuits according to the magnitude of impedance of a DC power supply, depending on the commutation type. The user selects the most suitable one of these various inverter circuits according to the DC power source and the AC load. For example, the voltage type inverter circuit can equivalently control the AC output voltage by combining with the PWM control, and can also perform the current control by utilizing the high speed control capability of the PWM control. ing. This type of PWM-controlled voltage-type inverter circuit has been used to enable vector control of an induction motor, and the range of use of an inexpensive and robust induction motor has expanded dramatically.

Further, in the current type inverter circuit, if a voltage control loop is added to form an inverter circuit for an induction motor with a constant V / f, the four quadrant operation can be performed without any other special circuit. This makes it possible to easily save energy by regenerating load energy to the power source.

[0004]

However, the above-mentioned various conventional inverter circuits have not yet solved the following problems. As described above, various conventional inverter circuits aim to achieve higher functionality by adding a PWM control circuit and a voltage control loop to the basic circuit configuration as an inverter circuit, and to configure a more advanced power control circuit. It has been developed with a focus on it. Therefore, the inverter circuit configuration has become complicated, the cost has increased with an increase in the number of parts, and the reliability thereof has deteriorated. Further, when a complicated inverter circuit is used, the circuit adjustment depending on the AC load becomes complicated and the versatility becomes poor.

By the way, considering general electric loads such as lighting of fluorescent lamps and rotation control of electric fans, most of them are capacitive or inductive AC loads.
Most of them do not require the highly functional inverter circuit as described above. That is, a general electric load can be sufficiently driven only by the function of converting DC power to AC power, which is achieved only by the basic circuit configuration of the inverter circuit, and shaping of voltage and current waveforms, voltage and current Rough control of the magnitude relationship and phase relationship of is sufficient.

With respect to most of the AC loads as described above, it cannot be said that various conventional inverter circuits provide optimum circuits. Rather, they have excessive performance, so that the price / performance ratio is significantly reduced. There is a problem such as that.

The inverter circuit of the present invention aims to solve these problems, achieve the basic function of an inverter for driving a general AC load with a simple structure, and greatly improve the price / performance ratio. Was made as
The following composition was adopted.

[0008]

The inverter circuit of the present invention converts DC power into AC power of a desired frequency by using a switching element that is turned on / off by a switching signal, and drives the AC load with the AC power. In the inverter circuit, there is provided a microprocessor for outputting the switching signal from a digital output port, and an input means for inputting a state quantity relating to the AC load to an analog input port of the microprocessor, A program executed by a microprocessor, the storage means for storing a load control program for changing a switching cycle of the switching signal based on a state quantity input from the input means is provided in the microprocessor. Use as a summary.

[0009]

In the inverter circuit of the present invention configured as described above, the switching element is driven by the switching signal output from the digital output port of the microprocessor, and the DC-AC converted AC power is supplied to the AC load. Given. The state quantity relating to the AC load, such as the load fluctuation, the target load or the ON / OFF instruction, is input to the analog input port of the microprocessor by the input means. Further, a load control program for changing the switching cycle of the switching signal based on the state quantity input from the input means is stored in the storage means in the microprocessor, and the microprocessor executes this program. Therefore, the AC load can be controlled based on the state related to the AC load by a simple circuit using a microprocessor.

Here, the state quantity relating to the AC load controlled by the load control program is a broad concept including not only the power consumption of the AC load but also the target load. The target load does not have to be a fixed value either, and can be changed appropriately by the user's operation, or sequence control can be performed according to a predetermined procedure in advance, or the microprocessor can be set according to detection signals from various sensors. To calculate,
Various ways of giving can be considered.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the inverter circuit of the present invention will be described below in order to further clarify the structure and operation of the present invention described above. FIG. 1 is a block diagram of an electric circuit when the inverter circuit 20 of the embodiment is used as a dimming circuit of a fluorescent lamp 50. As shown in the figure, the inverter circuit 20 is mainly composed of a one-chip microprocessor (hereinafter referred to as MPU22), and its two digital output ports PD1 and PD2 are n-channel FET1 and FET2 via resistors R1 and R2, respectively. Connected to the gate (G).

The source (S) of the FET1 and the drain (D) of the FET2 are connected to each other, and this connection point is also connected to one electrode of the fluorescent lamp 50 which is a load. Therefore, the drain of FET1 is used as a positive potential DC power source
The source of 2 is connected to the DC power source of negative potential, and these FETs
Output ports PD1 and PD for the gates of FET1 and FET2
If the gate signal is given exclusively from 2, the fluorescent lamp 50
AC power can be supplied to. In this embodiment, in order to easily obtain a DC power source of positive / negative potential, the diode D
A half-wave rectifier circuit 30 composed of 1, D2 and capacitors C1, C2 is connected to an AC power supply AS.

The other electrode of the fluorescent lamp 50 is grounded via a current detecting resistor R3 having a small resistance value. The resistor R3 is connected to the analog input port PA1 of the MPU 22, and the voltage drop value according to the load current i of the fluorescent lamp 50 is input to the MPU 22.

Other input ports PO1 and PO of MPU22
Reference numeral 2 is connected to an output terminal of a known remote control receiving element 26 that outputs a reception signal corresponding to a detection signal of the infrared sensor 24 and an output terminal of a touch sensor 28. Here, the touch sensor 28 extends a contact piece to the outside as a part of the electric circuit, and outputs from the output terminal the internal state of the electric circuit which changes when a high impedance body such as a human body touches the contact piece. It is a known one.

The DC power source of the MPU 22 configured as above is obtained from the DC power source of the positive potential of the half-wave rectifier circuit 30 as follows. Resistor R is a positive potential DC power supply
4 and the variable resistor VR to divide the voltage, and the voltage dividing point and MPU2
The second power supply port VD is connected. Then, two diodes D3 and D are provided between the power supply port VD and the ground.
4 are connected in series to limit the maximum potential of the power supply port VD to a value equal to the voltage drop of these diodes D3, D4.
Further, in order to suppress the pulsation of the DC potential of the power supply port VD, a large capacity electrolytic capacitor C4 is connected to the power supply port VD.

The variable resistor V used in this embodiment is
The R is a type whose resistance value can be changed by software according to the voltage value applied to the intermediate tap, and the analog output port PV1 of the MPU 22 is connected to the intermediate tap. Therefore, the resistance value of the variable resistor VR can be freely controlled from the MPU 22, and by controlling the resistance value optimally, the current flowing into the diodes D3 and D4 can be suppressed as small as possible, the rated capacity is small, and the cost is low. The diode element can be used.

When the inverter circuit 20 of the present embodiment configured as described above is connected to the positive voltage output side of the half-wave rectification circuit 30, DC power is supplied to the MPU 22, and the MPU 22 is supplied.
22 is activated. This MPU 22 has an RO inside
Internal ROM with built-in M, RAM, timer, etc.
A control program showing the flowchart of FIG. 2 is stored in advance. The MPU 22 is designed to repeatedly execute this control program immediately after starting.
The operation of the inverter circuit 20 of this embodiment will be described below with reference to the flowchart of FIG.

When the MPU 22 is activated by the connection with the DC power source, a hard check of each of the above-mentioned circuit components and the internal RAM and the count value X of the internal counter CK is set to the initial value S.
Initial processing such as setting to (step 10
0). Next, at the cycle T corresponding to the count value X of the internal counter CK (X = S immediately after startup), the output ports PD1, PD
2 exclusively outputs the gate signal (step 11)
0). The relationship between the count value X of the internal counter CK and the cycle T of the gate signal is shown in FIG. As shown in the figure, since the count value X of the internal counter CK and the cycle T are set in a substantially directly proportional relationship, the cycle T becomes longer as the count value X becomes larger. That is, since the ON / OFF cycle T of the FET1 and FET2 becomes long, the frequency f (= 1 / T) of the AC power supplied to the fluorescent lamp 50 becomes low and the brightness thereof decreases.

After determining the approximate period T of the gate signal in this way, it is judged whether or not there is information input from the input ports PO1 and PO2 (step 120), and when it is judged that there is information input, the external input. The count value X is updated (step 130) and the target brightness VS is updated (step 140). Here, the target brightness VS
Is a value corresponding to the voltage generated at both ends of the resistor R3 by the current i flowing through the fluorescent lamp 50 when the fluorescent lamp 50 is lit with the brightness determined in advance according to the external input. That is, when the target brightness of the fluorescent lamp 50 is changed by the external information input from the remote control receiving element 26 and the touch sensor 28, the FE is detected at the cycle T corresponding to the target brightness VS.
The count value X is immediately updated to switch T1 and FET2, and at the same time, the target brightness VS is updated in preparation for the feedback control described later. When this series of processes is completed, the process returns to step 110. Therefore,
The cycle T of the switching signals from the digital output ports PD1 and PD2 is changed to a value according to external information, and the brightness of the fluorescent lamp 50 is changed.

On the other hand, when it is determined in step 120 that there is no external information input, that is, when there is no demand for changing the brightness, steps 150 and 160 are executed instead of steps 130 and 140. In step 150, the magnitude relationship between the voltage value Vi input from the analog input port PA1 and the target brightness VS is determined.
Here, the input voltage value Vi is ± α (α
Is within the tolerance),
That is, when the actual brightness of the fluorescent lamp 50 is substantially equal to the target brightness VS, nothing is performed and the process returns to step 110. On the other hand, when it is determined in step 150 that the voltage value Vi deviates from the target brightness VS by more than the allowable error α, that is, when the actual brightness of the fluorescent lamp 50 largely deviates from the target brightness, this In order to eliminate the deviation, the count value X is increased or decreased (step 1
60) After that, the process returns to step 110, and the processes of steps 110 to 160 described above are repeated.

The inverter circuit 2 of this embodiment described above
0 has a basic function of an inverter that can drive a fluorescent lamp 50 that is an AC load by using a DC power source of positive / negative potential generated from commercial AC. Moreover, its basic function is MPU22 and FET1, which is a switching element.
Since it is composed of only the FET 2, an inexpensive and highly reliable circuit can be provided. In addition, the control program of the MPU 22 uses the load current i of the fluorescent lamp 50 in software.
By feeding back the brightness of the fluorescent lamp 50 to the target brightness VS
To control. Therefore, the fluorescent lamp 50 can be easily dimmed without adjusting complicated circuit elements.

Further, since the DC power supply of the MPU 22 which constitutes the inverter circuit 20 of this embodiment uses the DC power supply of the positive potential before being converted into the AC power supply by the inverter function, a separate power supply line is required. However, the circuit configuration is simpler. Even the power supply voltage of the MPU 22 is configured to be software-controllable by the MPU 22, so no circuit adjustment is required.

The dimming of the fluorescent lamp 50 is instantaneously executed by the count value X which is immediately updated according to the external information (steps 130 and 140). Therefore, by operating the infrared remote controller or the touch sensor 28, the fluorescent lamp 5
The brightness of 0 can be changed instantaneously. Moreover, since the feedback control of the load current i is executed thereafter (steps 150 and 160), the relationship between the cycle T and the target brightness of the fluorescent lamp 50 changes due to variations in the fluorescent lamp 50 and changes over time. However, the change is immediately absorbed, and the desired brightness can be obtained.

Although the power source of the MPU 22 is directly obtained from the DC power source of the inverter circuit 20 in this embodiment, a dedicated DC power source may be prepared. Further, in this embodiment, the relationship between the count value X of the internal counter CK and the cycle T is fixed by the characteristic shown in FIG. 3, but this relationship is learned in order to improve the control responsiveness to the time change of the AC load. It may be updated. In this case, MPU2
The characteristic diagram shown in FIG. 3 may be stored in the RAM area backed up by the power supply as 2, and the characteristic diagram may be updated based on the feedback value of the load current i.

The embodiment of the present invention has been described above.
The present invention is not limited to these embodiments at all, and is configured to control loads other than fluorescent lamps, to change loads according to a pre-defined sequence, and to utilize other input / output ports of MPU 22 to provide a single A configuration in which a plurality of AC loads are individually controlled by the MPU 22, a host computer is connected to the serial communication port of the MPU 22 to form a centralized management system, and each load is controlled by a command from the host computer, etc. deviates from the gist of the present invention. It goes without saying that the present invention can be carried out in various modes.

[0026]

As described above, according to the inverter circuit of the present invention, according to the load control program stored in the microprocessor, the digital signal of the microprocessor is generated based on the state quantity related to the AC load input to the analog input port. The switching element is directly driven from the output port to control the AC load. Therefore, the basic function of the inverter can be realized with a simple circuit configuration, and the price / performance ratio can be greatly improved.
However, it is possible to realize an inverter circuit that does not require complicated circuit adjustment and is excellent in versatility.

[Brief description of drawings]

FIG. 1 is a block diagram of an electric circuit of an inverter circuit according to an embodiment of the present invention.

FIG. 2 is a flowchart of a control program for the inverter circuit.

FIG. 3 is an explanatory diagram of a relationship between a count value X and a cycle T used in the control flowchart.

[Explanation of symbols]

 20 ... Inverter circuit 22 ... MPU 24 ... Infrared sensor 26 ... Remote control receiving element 28 ... Touch sensor 30 ... Half-wave rectification circuit 50 ... Fluorescent lamp

Claims (1)

[Claims] 1. An inverter circuit for converting DC power into AC power of a desired frequency by using a switching element that is turned on / off by a switching signal and driving an AC load with the AC power, wherein the switching signal is digitally output. For the microprocessor that outputs from the port and the analog input port of the microprocessor,
An input unit for inputting a state quantity relating to the AC load; and a program executed by the microprocessor, wherein the switching cycle of the switching signal is changed based on the state quantity input from the input unit. An inverter circuit having a storage means for storing a load control program for controlling the inside of the microprocessor.