JPH0714274B2 - AC power control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention converts DC power into AC power, performs intermittent control when supplying the AC power to a load, and even supplies an effective value thereof. The present invention relates to a variable AC power control circuit.

[Prior Art] Conventionally, various inverter circuits for driving various AC loads such as an AC motor with a DC power supply have been proposed. For example, in order to control the speed of an electric motor with high efficiency, it is necessary to supply AC electric power having a desired frequency and an effective value to the electric motor. According to the inverter circuit, the frequency of the AC power can be controlled easily by changing its operating frequency, and the effective value of the AC power can be easily controlled by interrupting its operation (so-called PWM control). Can be controlled.

As is well known, the useful inverter circuit as described above is configured by a bridge connection of high-speed switching elements, and the inverter operation is performed by selectively ON / OFF controlling these switching elements. In recent years, power MOS FETs (hereinafter referred to as MOS
The one that adopted (T) came to appear. This MOS
If an inverter circuit that uses T is applied to motor control, it is clear that it has the following excellent features.

First, since the switching speed of the MOST is extremely high, high efficiency, low noise and miniaturization of motor control can be achieved.

Secondly, since the MOST is a voltage control type switching element, power saving and simplification of the control circuit can be achieved.

Third, since the current characteristic of the MOST exhibits a negative temperature coefficient, it is easy to increase the capacity by parallel connection.

Fourthly, the diode built in between the drain and source of the MOST has extremely high performance and can be used as a conventional flywheel diode. Etc.

[Problems to be Solved by the Invention] However, even the above-described inverter circuit using the MOST is not sufficient, and has the following problems.

P-MO that uses P-type semiconductor as a channel for MOST
There are two types: S FET (hereinafter referred to as P-MOST) and N-MOS FET (hereinafter referred to as N-MOST) that uses N-type semiconductors. Both of these two types of MOST have highly efficient operating performance,
If it can be easily manufactured, it is possible to use a complementary configuration that uses both of them, simplifying the inverter circuit,
Miniaturization is easy.

However, as is well known, the P-MOST has disadvantages such as a large voltage drop compared to the N-MOST, so its utilization rate is low, and an inverter circuit is configured using only the N-MOST. Always. To turn on this N-MOST, N-MOST
A gate voltage of several V is applied between the source and the gate of the N-MOST, but when the drain of the N-MOST is connected to the + side of the DC power supply, the source potential is also a high potential approximately the same as the DC power supply potential. Therefore (drain-source voltage drop is small), a higher-potential voltage source other than the DC power supply is required to obtain the control voltage applied to the gate. This is a factor that increases the number of components of the inverter circuit that uses N-MOST, and has been a cause that prevents the circuit from becoming smaller and lower in cost.

The present invention has been made in view of the above problems, by configuring an inverter circuit using N-MOST or the like, further simplify the control circuit to obtain the AC power of a desired frequency and effective value,
It is an object of the present invention to provide an excellent AC power control circuit that is small in size and low in cost.

[Means for Solving Problems] According to the configuration of the present invention for solving the above problems, a control signal connected to an electric circuit of a controlled system and having a higher potential than a potential of a DC power source by a predetermined value or more is applied. An inverter unit having a switching element for electrically connecting a DC power supply to an electric circuit of the controlled system, and a switching element of the inverter unit based on an oscillation signal from an oscillation circuit having a predetermined oscillation frequency higher than the operating frequency of the inverter unit. By interrupting the operation of, a PWM control unit for controlling the AC power supplied to the electric circuit of the controlled system connected to the inverter unit, a pumping capacitor and a smoothing capacitor,
The oscillation signal of the oscillation circuit is input, and at the timing synchronized with the frequency of the oscillation signal, a voltage obtained by boosting the power supply voltage is generated in the pumping capacitor by a pumping action, and the smoothing capacitor is generated by the boosted voltage. And a booster circuit for charging the capacitor, and an output from a smoothing capacitor in the booster circuit is appropriately used as a control signal for a switching element of the inverter section.

[Operation] In the AC power control circuit according to the present invention, the inverter section is connected to an electric circuit of the controlled system, and is composed of a switching element which conducts when a control signal having a potential higher than that of the DC power supply is applied. Has been done.

Further, the control circuit for alternating-current power according to the present invention has a PWM control unit that changes the effective value of the power supplied to the electric circuit of the controlled system, and a booster circuit that boosts the voltage of the DC power supply.

The PWM control unit interrupts the operation of the switching element of the inverter unit based on an oscillation signal from an oscillation circuit having a predetermined oscillation frequency higher than the operating frequency of the inverter unit, thereby supplying power to the electric circuit of the controlled system. PWM control is performed by changing the effective value of.

The booster circuit also has a pumping capacitor and a smoothing capacitor, inputs the oscillation signal used for PWM control, and boosts the DC power supply voltage to the pumping capacitor by the pumping action at the timing synchronized with the oscillation frequency. Is generated and the smoothing capacitor is charged by the boosted voltage.

The output from the smoothing capacitor thus charged to a higher potential than the DC power supply voltage is used as a control signal for the switching element of the inverter section.

Hereinafter, in order to describe the present invention more specifically, examples will be described in detail.

[Embodiment] FIG. 1 shows an N-MO having excellent features when used as a speed control circuit of an AC motor M as described above.
It is an electric circuit diagram which constituted the alternating current power control circuit using six ST (Q1-Q6). Three sets (Q1, Q4, Q2, Q5, Q3, Q6) in which two N-MOSTQNs (N = 1 to 6) are connected in series are connected in parallel to the DC power supply VDC. This is a normal three-phase bridge configuration in which electric power is supplied from the intermediate point to each phase input terminal of the three-phase electric motor M. As we all know, N-
The MOSTQN is conductive between the drain and the source only when a potential higher than the source potential by 5 to 6 [V] is applied to the gate. Therefore, in N-MOSTQN, the lower element of the three-phase bridge whose source potential is the ground level, N-MOSTQN
Gate terminals of 4, Q5, Q6 are resistance to + line of DC power supply VDC
It is pulled up via R4, R5, and R6. On the other hand, the source potential of the upper elements N-MOSTQ1, Q2, Q3, of the three-phase bridge in the conductive state is a high potential that is several [mV] lower than the drain connected to the + side line of the DC power supply, The voltage applied to the gate cannot be obtained from the same DC power supply VDC because it is conductive. Therefore, in this embodiment, the gate terminals of these N-MOS TQ1, Q2, and Q3 are pulled up from the output line of the booster circuit 10 described later via the resistors R1, R2, and R3. Since the N-MOSTQNs whose gate terminals are pulled up as described above are always in the conductive state as they are, the gate terminals of the N-MOSTQNs of the gate drive circuit 20 that simultaneously take the switching timing to achieve the invert function. It is also connected to the control terminal. The control terminal of the gate drive circuit 20 is an output terminal of open collector type, and can take two levels of ground level or open. Therefore, when the control terminal of the gate drive circuit 20 is at the ground level, the N-MOSTQN is in the cutoff state, and the N-MOSTQN is conductive only when the control terminal is in the open state.

The timing at which the gate drive circuit 20 turns on / off each N-MOSTQN is a normal timing at which three-phase alternating currents having different phases by (2/3) π are applied to the electric motor M. .

The gate terminals of the three-phase bridge lower side devices N-MOSTQ4, Q5, Q6 of the present embodiment are the switching transistors T of the NPN type.
It is also grounded via r4, Tr5, Tr6. Therefore, when a signal is input to the bases of the switching transistors Tr4, Tr5, Tr6, even if the control terminal of the gate drive circuit 20 is in the open state and the N-MOSTQ4, Q5, Q6 are in the conductive state, it is not affected by it. Then, it is possible to change the N-MOS TQ4, Q5, Q6 to the cutoff state. That is, when the gate circuit 34 allows the oscillation signal of the square wave oscillator circuit 32 to pass, the switching transistors Tr4, Tr5, Tr6 which are the control elements of the PWM circuit 30.
Thus, PWM control of three-phase AC synchronized with the oscillation signal of the square wave oscillator circuit 32 is realized. The gate circuit 34 opens its gate only when a high level signal is applied to the control terminal CP.

The output of the square wave oscillator circuit 32 of the PWM circuit 30 is P
In addition to the WM circuit control, the voltage is also input to the booster circuit 10. Further, if a signal with a duty of 50% is desired as a signal to the booster circuit 10, for example, if the frequency division is performed, a signal with a duty of 50% is obtained. This booster circuit 10 is configured as a well-known pumping circuit, and when the output of the square wave oscillator circuit 32 is at a low level, the transistor Tr1 is turned off and Tr2 is turned on, and the diode D1 is turned on.
The capacitor C1 as a pumping capacitor is charged to the power supply voltage of the DC power supply VDC with the polarity shown in FIG. Next, when the output of the square-wave oscillator circuit 32 becomes High level, the transistors Tr1 and Tr2 are inverted and the transistor Tr1, the capacitor C1 and the diode D2 are inverted.
Through this, the capacitor C2 as a smoothing capacitor is charged. Therefore, the capacitor C2 will always be charged with a voltage of about twice the DC power supply voltage (slightly lower by the forward voltage drop of the diodes D1 and D2) with the polarity shown in the figure, thus achieving the purpose of boosting. As described above, it serves as a voltage source that pulls up the gates of the upper elements N-MOSTQ1, Q2, Q3 of the three-phase bridge. At this time, the current i that can be extracted from the capacitor C2 is i = C × (VB−VF) × F ... where C: capacitance of the capacitor C1 VB: voltage of the DC power supply VDC VF: forward voltage drop of the diode F: Represented by the oscillation frequency of the square wave oscillator. N-MOS TQ driven by capacitor C2
1, Q2, Q3 are voltage control type FETs, and since they consume less power, they are sufficient voltage sources.

It is apparent that the AC power control circuit of this embodiment configured as described above has the following actions and effects.

First, the inverter circuit that performs DC-AC conversion is
It is the same as the one using N-MOST, and operates at high speed and high efficiency with low power consumption as described above.

Secondly, since the PWM circuit 30 is provided, it is possible to supply the AC power corresponding to the mechanical load of the electric motor M, and the electric motor control efficiency can be further improved.

Furthermore, as a third point, N-MO that is optimal as an inverter circuit
Despite using only the ST element, the booster circuit 1 that uses the oscillation signal of the PWM circuit 30 for the high voltage for its gate drive.
It is supplied from 0. That is, the booster circuit 10 charges the capacitor C2 according to the oscillation signal of the square wave oscillator circuit 32 having an oscillation frequency higher than the drive frequency of the gate drive circuit 20 to boost the voltage of the DC power supply VDC. Therefore, in this embodiment, as can be understood from the above-mentioned formula, by using a signal of a higher frequency in the booster circuit, a small-capacity pumping capacitor can be obtained without changing the amount of current that can be taken out. , The downsizing of the booster circuit, the downsizing of the AC power control circuit, and the reduction of the circuit cost.

In the above embodiment, the PWM circuit 30 is constructed by using the new switching elements and the switching transistors Tr4, Tr5, Tr6, but the gate drive circuit 20 is used to directly control ON / OFF of the N-MOS TQN. May be. In addition, the PWM circuit 3
Although the operating condition of 0 is determined by the control terminal CP input of the gate circuit 34, a triangular wave oscillation circuit or the like may be adopted instead of the square wave oscillation circuit 32 as shown in FIG. When this is done, the output to the booster circuit 10 is the result of comparison with the voltage E1 that is 1/2 times the maximum value of the triangular waveform, that is, a square wave with a duty ratio of 50% is output in the same manner as in the previous embodiment, and switching is performed. The outputs to the transistors Tr4, Tr5, Tr6 can produce a square wave with a desired duty ratio by adjusting EV as shown in the figure if the reference voltage EV to be compared can be adjusted.
PWM control by Tr5 and Tr6 can be controlled freely.

Although the embodiment has been described in detail by exemplifying the case of controlling a three-phase electric motor, the present invention is not limited to the three-phase AC control and can be applied to other multi-phase AC control, as well as the AC load (electric circuit of the controlled system). ) Is inductive, the diode built into the N-MOSTQN can be used as a flywheel diode and is extremely useful.

[Effects of the Invention] As described in detail with reference to the embodiments, the AC power control circuit of the present invention has high efficiency, high speed, and excellent switching characteristics, but is controlled by a DC power supply. The inverter unit is configured using the N-MOST or the like that requires the above high voltage source. Then, in the booster circuit, an oscillation signal with a frequency higher than the operating frequency of the inverter unit used for PWM control is used, and at a timing synchronized with the oscillation frequency, a voltage obtained by boosting the DC power supply voltage to the pumping capacitor by the pumping action is generated. Then, the smoothing capacitor is charged by the boosted voltage. The output of the smoothing capacitor thus charged at a voltage higher than the DC power supply voltage is used as a control signal for the switching element of the inverter unit such as N-MOST.

Therefore, the AC power control circuit according to the present invention is based on a reduction in the capacity of the pumping capacitor and the like by using the oscillation signal of a frequency higher than the operating frequency of the inverter unit in the booster circuit including the capacitor. Miniaturization of booster circuit, and eventually miniaturization of control circuit for AC power,
It is possible to realize cost reduction due to the miniaturization.

[Brief description of drawings]

FIG. 1 is a schematic electric circuit diagram of an AC power control circuit according to an embodiment of the present invention, and FIG. 2 is an explanatory view of another embodiment for giving a PWM control timing in the embodiment. Q1 to Q6 ... N-MOSTM ... Motor 10 ... Booster circuit 20 ... Gate drive circuit 30 ... PWM circuit

Claims (1)

[Claims] 1. A switching element, which is connected to an electric circuit of a controlled system and electrically connects the electric circuit of the controlled system and a DC power source when a control signal having a potential higher than a predetermined value by a DC power source is applied. And an inverter unit having a predetermined oscillating frequency higher than the operating frequency of the inverter unit to interrupt the operation of the switching element of the inverter unit based on an oscillating signal from the oscillating circuit. It has a PWM control unit for controlling the AC power supplied to the electric circuit of the control system, a pumping capacitor and a smoothing capacitor,
The oscillation signal of the oscillation circuit is input, and at the timing synchronized with the frequency of the oscillation signal, a voltage obtained by boosting the power supply voltage is generated in the pumping capacitor by a pumping action, and the smoothing capacitor is generated by the boosted voltage. A control circuit for alternating-current power, comprising: a booster circuit for charging the battery; and an output from a smoothing capacitor in the booster circuit is appropriately used as a control signal for a switching element of the inverter section.