JPS6162394A - Controller for inverter - Google Patents

Abstract

PURPOSE:To reduce the cost and to accurately control by controlling an inverter by a pulse width modulation signal with the prescribed duty cycle as a reference. CONSTITUTION:A motor current flowed to an inverter IV is detected by a current detector ID, amplified by an amplifier A5, as a signal having 180 deg. different phase to an inverting amplifier A6. A PWM signal from a comparator A3 and a 50% duty cycle rectangular wave form a comparator A4 are compared in phase by a phase comparator PD to discriminate whether the duty cycle of the PWM signal is larger than 50% or not, switches SW1, SW2 are switched by the discriminated result to input the output signal of an amplifier A5 or A6 to a current indicating amplifier A2.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an inverter control circuit used for controlling an electric motor.

Conventional technology When controlling a motor by detecting the current of the motor in an inverter control circuit, as shown in FIG. 4, transistors Qll, Q12 are on and transistors Q13, Q13,
When Q14 is off, the voltage generated across resistor R32 is used to detect the current of motor M, and transistors Q13,
When Q14 is on and transistors Qll and Q12 are off, the voltage generated across resistor R31 is used to detect the current of motor M. The difference between the voltages generated across resistors R31 and R32 is then applied to operational amplifier 0P11 and resistor R.
The amount and direction of the current are detected by a differential amplifier consisting of R33 to R36. A current detection element such as a current detection transformer may be used as the current detection resistors R31 and R32.

Problems to be Solved by the Invention In the above inverter control device, the forward and reverse currents flowing through the motor are detected and the difference is taken, so two current detection elements must be used, resulting in high cost. Become.

In addition, as shown in Figure 5, the torque and current of the motor are proportional. If the resistors R31 and R32 are not equal, the gain of the detection output will not be the same for the forward current and reverse current of the motor, which will reduce the reliability of the motor control. decreases.

Means for Solving the Problems The present invention provides an inverter circuit that converts the output from a DC power supply into a multi-phase AC voltage to supply current in the forward and reverse directions to a motor, and an inverter circuit between the inverter circuit and the DC power supply. a current detection element that detects the current flowing through the inverter circuit, and a pulse width modulation (hereinafter referred to as PWM) signal based on a constant date cycle signal to determine the current direction of the motor. A PWM control circuit for controlling the PWM signal inverter circuit, an amplifier circuit for amplifying the output signal of the current detection element to generate inverted and non-inverted signals, and the first and second amplifier circuits. a switching circuit that feeds back one of the inverted and non-inverted signals to the PWM control circuit; and a switching circuit that determines whether the duty cycle of the PWM signal is larger or smaller than the constant duty cycle, and switches the switching circuit according to the result of this determination. and a duty cycle determining means for controlling.

A working PWM control circuit generates a four-layer signal based on a constant date cycle signal to determine the direction of energization of the motor;
In response to this PWM signal, the inverter circuit converts the output from the DC power supply into a multi-phase AC voltage, and supplies current in the forward and reverse directions to the motor. The current flowing through the inverter circuit is detected by a current detection element, and its output signal is amplified by an amplifier circuit to generate inverted and non-inverted signals. The duty cycle determining means determines whether the duty cycle of the PWM signal is larger or smaller than the constant duty cycle, and depending on the result of this determination, the switching circuit selects one of the inverted and non-inverted signals generated by the amplifier circuit to the PWM control circuit. to return to.

Embodiment FIGS. 1 and 2 show an embodiment of the present invention, and FIG. 3 is a timing chart thereof.

Speed error amplifier A1 is operational amplifier OPI, capacitor C
1 and resistors R1 to R4, and amplifies the error between the speed reference input and the output signal of the frequency/voltage converter f/V and outputs it as a motor current instruction signal. Current indicating amplifier A2 is operational amplifier OP2. Capacitor C2 and resistor R5
~R8, and the output voltage of the speed error amplifier A1 instructs the amount of current to flow to the synchronous motor SM, and this current amount actually flows to the synchronous motor SM! Amplify the error with the flow rate. Triangle wave oscillator O8
C is a reference oscillator that generates a triangular wave. The comparator A3 is composed of an operational amplifier OP3 and resistors R9 and RIO, and together with the current indicating amplifier A2 constitutes a PWM control circuit, and compares the output signal of the current indicating amplifier A2 with the triangular wave from the triangular wave oscillator O8C to generate a PWM signal. Create. Comparator A4 is operational amplifier OP4 and resistor R11
, R12, and compares the triangular wave from the triangular wave oscillator O8C with the ground potential to convert it into a rectangular wave with a data cycle of 50%.

The pulse generator PG generates a pulse signal having a frequency proportional to the rotation speed of the synchronous motor SM and a phase difference of 90° depending on the rotation direction of the motor SM. frequency/
The voltage converter f/V converts the output pulse signal of the pulse generator PG into a signal whose polarity changes depending on the rotational direction of the motor SM and whose voltage changes depending on the speed of the motor SM. The level shift amplifier A5 is constituted by an operational amplifier OP5 and resistors R13 to R16, and level-shifts the signal of the Hall element H to the ground level and amplifies it. The inverting amplifier 6 is composed of an operational amplifier OP6 and resistors R17 to R19, and amplifies the output signal of the level shift amplifier A5 by a factor of 11. The phase comparator PD is a NAND circuit NAI.

Flip 70-tube FF consisting of NA2 and NAND circuit NA
3. It is composed of NA4, inverters Nl and N2, and compares the phase of the PWM signal from comparator A3 and the square wave with a duty cycle of 50% from -xnhalator A4, and turns on analog switches SWI and SW2.
Turn it off. That is, the PWM signal from the comparator A3 is inverted by the inverter N2, and the NAND circuit NA4 takes a 50% duty cycle square wave from the comparator A4 and the NAND signal, and at the same time, the rectangular wave from the comparator A4 is inverted by the inverter N1. Nando circuit NA3
By taking the NAND with the PWM signal from comparator A3, the phases of the PWM signal from comparator A3 and the rectangular wave from comparator A4 are compared, and P
It is determined whether the duty cycle of the WM signal is greater or less than 50%. The output signal (2) of the NAND circuit NA4 becomes a pulse signal if the duty cycle of the PWM signal is less than 50 times, otherwise it remains at a high level. The output signal 0 of the NAND circuit NA3 becomes a pulse signal if the date cycle of the PWM signal is greater than 50%, and otherwise remains at a high level. The flip-flop FF is set at the falling edge of the output pulse of the NAND circuit NA4 and reset at the falling edge of the output pulse of the NAND circuit NA3, so that the duty cycle of the PWM signal is 5.
Output signals ◯ and ◯ indicating whether 0 is smaller or larger are output to turn on/off the switches SWI and SW2. The pole sensor PS detects the rotor position of the mechanical motor SM. The inverter control section SL, which consists of a 120° switching logic circuit, is a ball sensor P.
The output signal of S and the PWM signal from comparator A3 are combined to create a gate signal, and this signal is used to connect the inverter circuit I via an isolation amplifier such as a photocoupler.
N is controlled to control the energization of the motor SM. The inverter circuit IN is constituted by field effect transistors Q1 to Q6, converts the DC output of the converter Cv into a three-phase AC voltage, and supplies current to the motor SM. This inverter circuit IV operates in synchronization with the output signal phase of the ball sensor PS by turning on and off the field effect transistors Q1 to Q6 with gate signals from the inverter control unit SL, and operates in a direction and amount according to the PWM signal. energize the motor SM.

The converter Cv is constituted by a diode bridge circuit DB and a capacitor C3, and converts input from an AC power supply AC such as a commercial television to DC. The current detector ID is an isolation current detector constructed by winding an electric wire W around a C-shaped core CR and placing a Hall element H in the gap of the core CR.The electric wire W connects an inverter circuit IV and a converter C■
A current is supplied to the Hall element H from a current source CC. The current flowing through the inverter circuit IV also flows through the electric wire W, generating a magnetic field, which is transmitted to the Hall element H.
Detected in

Next, the operation of this embodiment will be explained.

The speed reference input applied from the outside, the motor speed signal from the frequency/calculator pressure converter f/v, and the error are amplified by the speed error amplifier A1 and output as a motor current instruction signal, and this motor current instruction signal and the motor SM The error in the actual current is amplified by the current indicating amplifier A2. The output signal of the current indicating amplifier A2 is compared with the triangular wave from the triangular wave oscillator O8C by the comparator A3 and becomes a PWM signal.
It is added to an inverter control section SL consisting of a 120° switching logic circuit. The inverter control unit SL performs a logical operation on the motor rotor position signal generated by the pole sensor PS and the PWM wave from the comparator A3, and synthesizes the gate signals of the field effect transistors Q1 to Q6.

This gate signal turns on/off the field effect transistors Q1 to Q6 of the inverter circuit IV through an isolation amplifier, and the DC voltage from the converter Cv is converted into a three-phase AC voltage by the inverter circuit IV, and the motor SM
is energized.

The current detector ID detects the motor current flowing through the inverter circuit IV, and a voltage proportional to the amount of current is detected by the Hall element H.
It occurs. This voltage is shifted to the ground level and amplified by the level shift amplifier A5, and further amplified by υ-1 times by the inverting amplifier A6, resulting in signals having a phase difference of 180°.

Level shift amplifier A5. One of the output signals of the inverting amplifier A6 is selected by the switches SWI and SW2 and fed back to the current indicating amplifier A2. Konno Kurator A3
pw from? , q signal and the rectangular wave of 50 data cycles from the comparator A4 are compared in phase by a phase comparator PD to determine whether the data cycle of the PWM signal is larger or smaller than the 50 factor. Switches SWI and SW2 are switched.

Effects of the Invention As described above, according to the present invention, only one current detection element is required for detecting the current flowing through the inverter circuit, making it possible to reduce costs and reduce the number of peripheral circuits. Furthermore, there are fewer adjustment points, which improves maintenance and reliability. Also, U phase with 3 phase motor.

A method has been considered in which the phase current is detected and the W phase current is synthesized from these currents, but compared to this method, there are fewer errors and highly accurate control is possible.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram specifically showing the embodiment, Fig. 3 is a timing chart of the embodiment, and Fig. 4 is a circuit showing a conventional circuit. FIG. 5 is a diagram showing the torque versus current characteristics of the motor. IV...inverter circuit, ID...current detection element,
A2, A3-PWM control circuit, A5, A6 ・
...Amplification circuit, SWI, SW2...Switching circuit, P
D: Phase comparator for determining data cycle.

Claims (1)

[Claims] An inverter circuit that converts the output from a DC power supply into multi-phase AC voltage and passes current in the forward and reverse directions to the motor, and an inverter circuit that is interposed between this inverter circuit and the above DC power supply and detects the current flowing to the above inverter circuit. a current detection element,
a pulse width modulation control circuit that generates a pulse width modulation signal based on a signal with a constant duty cycle to determine the current direction of the motor, and controls the inverter circuit using the pulse width modulation signal; and an output of the current detection element. an amplifier circuit that amplifies a signal to produce inverted and non-inverted signals; a switching circuit that feeds back one of the inverted and non-inverted signals produced by the amplifier circuit to the pulse width modulation control circuit; and the pulse width modulation signal. an inverter control circuit comprising: duty cycle determining means for determining whether the duty cycle of the inverter is larger or smaller than the constant duty cycle, and controlling the switching circuit based on the result of this determination.