JPH04322171A - Inverter power supply apparatus - Google Patents

Abstract

PURPOSE:To provide a condition that amplitude of the reference sine wave signal includes relatively large carrier signal in order to suppress drop of output voltage, if a comparatively large load is applied, by suppressing amplitude of the carrier signal to a small value. CONSTITUTION:Since a load becomes large, an output voltage drops. Therefore an output voltage is detected and is then applied to a microcomputer 6 for compensation of the output voltage. The microcomputer 6 selects a lower value as a setting value of the upper limit comparator 2 and lower limit comparator 3 and makes small the amplitude of the carrier signal T. Thereby, a very long ON period occurs on the PWM wave signal and a mean voltage rises. Thereby, in a certain condition, amplitude of the reference sine wave signal relatively exceeds the amplitude of the carrier signal and the ON period of the PWM wave signal continues a longer time, preventing drop of the output voltage.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter power supply device.

0002

2. Description of the Related Art First, an overview of a conventional inverter power supply device will be explained. FIG. 6 shows a rectifying section and a switching section of an inverter power supply device that outputs a three-phase AC voltage for driving a motor. In FIG. 6, 31 to 36 are three-phase AC sources 37
Rectifiers 38a, 38b for full-wave rectification of AC voltage from
is a smoothing capacitor, and 39 to 44 are switching elements. A pair of switching elements, for example, switching elements 39 and 40 perform complementary switching and output power for one phase of the three-phase motor 45. U, V, and W are power supply lines for supplying three-phase AC power supply voltage to the motor 45, respectively, and the voltage is taken out from the connection point of the corresponding pair of switching elements. Switching element 3
9 and 40 are U phase, switching elements 41 and 42 are V phase,
The switching elements 43 and 44 are for W phase. 4
6 to 51 are diodes for energy feedback.

FIG. 7 shows the principle of operation. In FIG. 7, A, B, and C are reference sine wave signals for motor speed setting, and among these, the phase differences between signal A and signal B, signal B and signal C, and signal C and signal A are equal. It is 120 degrees.

[0004] T is a carrier signal, specifically a triangular wave voltage in which the voltage alternately increases and decreases linearly. The carrier signal T has a constant period. The reference sine wave signals A, B, and C and the carrier signal T are both input to a comparator, and a PWM wave signal is output from the comparator. The duty ratio of this PWM wave signal changes according to the cycles of the reference sine wave signals A, B, and C. Then, according to this PWM wave signal, the switching element 39
44, a voltage is generated between each current line U, V, W as shown in FIGS. 7 and 8, and the three-phase motor 45 is operated. 52-57 are drive circuits for driving the switching elements 39-44.

[0005] The output voltage is the reference sine wave signal A, B, C.
It is possible to switch by changing the amplitude of the triangular wave signal (carrier signal T) within the amplitude range of the triangular wave signal (carrier signal T). In other words, when lowering the output voltage, the reference sine wave signal A,
Compare the amplitudes of B and C to be smaller. On the other hand, when increasing the output voltage, the reference sine wave signals A, B,
Increase the amplitude of C. Normally, the amplitudes of the reference sine wave signals A, B, and C are changed and the output voltage is adjusted so that the ratio between the motor torque and the frequency of the output AC voltage is always constant.

[0006] Furthermore, the reference sine wave signals A, B, and C are digital signals converted into analog signals by a D/A converter, and their amplitude exceeds the power supply voltage (5V) of the D/A converter. There's nothing wrong. Further, the power supply voltage of the carrier signal generating section is also the same value (5V), and the amplitude of the output carrier signal is also approximately 5V. Therefore, even if the amplitude of the reference sine wave signals A, B, and C is increased in order to increase the output voltage, the amplitude will not exceed the amplitude of the carrier signal (5V). In other words, as shown in FIG. 10, when the amplitudes of the reference sine wave signals A, B, and C are relatively small compared to the carrier signal T, the reference sine wave signals A, B, and
The output voltage can be increased by increasing the amplitude of C, but as shown in Figure 9, the reference sine wave signals A, B,
When the amplitude of C reaches the same value (5V) as the carrier signal amplitude, the amplitudes of the reference sine wave signals A, B, and C cannot be increased any further.

[0007]

[Problems to be Solved by the Invention] The above configuration has the following problems. In other words, when a relatively large load is applied, the output voltage may drop. Normally, when power is supplied to a motor, if the mechanical load on the motor side is too large, a large amount of current will flow and the output voltage on the power supply side will drop. In order to increase the output voltage, it is possible to perform stabilization control by increasing the amplitude of the reference sine wave signals A, B, and C, but even if the amplitude of the reference sine wave signal is increased, the carrier will not be affected as described above. The maximum value of the signal will not be exceeded. Therefore, there is a limit to this method alone, and there is a problem that the output voltage decreases significantly when a certain amount of heavy load is applied.

The present invention has been made in view of the above-mentioned problems, and provides an inverter that can suppress output voltage drop even when the load increases and cannot be handled simply by increasing the amplitude of the reference sine wave signal. The purpose is to provide power supplies.

[0009]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides means for suppressing the amplitude of a carrier signal in accordance with the output current or output voltage.

0010

[Function] With the above configuration, even when a relatively large load is applied, the amplitude of the carrier signal is suppressed to a small value, so that the amplitude of the reference sine wave signal is relatively larger than the amplitude of the carrier signal. This makes it possible to increase the output voltage and maintain the output torque even under large loads.

[0011]

Embodiments Hereinafter, embodiments of the inverter power supply device according to the present invention will be described. Note that the configuration of the switching section of the inverter power supply device in this embodiment is the same as the configuration of the conventional example shown in FIG. 6, so detailed explanation thereof will be omitted.

FIG. 1 is a circuit diagram showing a carrier signal generation circuit of an inverter power supply according to this embodiment, and this inverter power supply has a carrier signal T generated by the carrier signal generation circuit shown in FIG. 1 and a carrier signal T shown in FIG. The switching element is controlled by a PWM signal obtained by comparing reference sine wave signals A, B, and C for motor speed setting.

In FIG. 1, 1 is an up/down counter, which has an 8-bit output terminal. QA, QB
~QH indicates the output terminal and output signal of the up/down counter 1. Up/down counter 1 counts up and down in response to clock signal CLK.

Reference numeral 2 denotes an upper limit comparator 2 that compares the up/down counter 1 with a setting signal from the microcomputer 6 during counting up. Further, 3 is a lower limit comparator that compares the up/down counter 1 with a setting signal from the microcomputer 6 during countdown. P0 to P7 indicate setting signals from the microcomputer 6 sent to the upper limit comparator 2 and the lower limit comparator 3. 4 represents an OR circuit, A and B represent inputs of the OR circuit 4, and Z represents an output of the OR circuit 4.

Reference numeral 5 denotes a JK flip-flop for switching between count-up operation and count-down operation. J and K are inputs of JK flip-flop 5, Q is JK
The output of flip-flop 5 is shown. The JK flip-flop 5 operates in response to the output signal of the OR circuit 4, and is configured such that the output Q is inverted every time J and K simultaneously rise to "Hi". The output Q of this JK flip-flop is sent to the up/down counter 1. This signal allows switching between count-up operation and count-down operation. Further, in the up/down counter 1, S1 is a signal terminal for determining whether to count up or count down the up/down counter 1, and the output signal Q of the JK flip-flop 5 is connected to this signal terminal S1. When S1 is "Low", up/down counter 1 counts up and S1
When is "Hi", up/down counter 1 counts down.

Reference numeral 7 denotes a D/A converter, which is provided with an 8-bit input terminal 9. The D/A converter 7 connects to this input terminal 9.
The up/down counter 1 is configured to output a voltage corresponding to the binary number input to the counter, and as mentioned above, the up/down counter 1 repeats counting up and down.
The output terminal of the D/A converter 7 outputs a triangular wave voltage, ie, a carrier signal T, having a slope corresponding to the tempo of the count-up and count-down described above. 8 is a comparator, which compares the carrier signal T output from the D/A converter 7 with reference sine wave signals A, B, and C, and
Outputs a WM wave signal.

Next, the functions of the upper limit comparator 2 and the lower limit comparator 3 will be explained in detail. During counting up, the upper limit comparator 2 compares the signal from the microcomputer 6 with the output signal of the up/down counter 1. During the countdown, the lower limit comparator 3 compares the signal from the microcomputer 6 with the output signal of the up/down counter 1. If the output value of the up/down counter 1 is different from the output value from the microcomputer 6 during counting up or down, the output signals of the upper limit comparator 2 and the upper limit comparator 2 will be "Lo".
It is "W". When the output value of the up/down counter 1 becomes the same as the output value from the microcomputer 6, the output signals of both comparators become "Hi". The signal is sent to the OR circuit 4. A and B are inputs of OR circuit 4, Z is OR
Represents the output of circuit 4. Table 1 is a truth table showing the operation of the OR circuit 4.

[0018]

[Table 1]

J and K of JK flip-flop 5 are 5
, and Q indicates the output of the JK flip-flop 5. J
The K flip-flop 5 operates in response to the output signal of the OR circuit 4, and is configured such that the output Q is inverted every time J and K simultaneously rise to "Hi". Table 2 is a truth table showing the operation of the JK flip-flop 5.

[0020]

[Table 2]

The output Q of the JK flip-flop is sent to an up/down counter 1, and this signal switches between a count up operation and a count down operation.

Assume that the count is currently in a count-up state. The up/down counter 1 performs a count-up operation according to the clock signal CLK. The output terminals QA, QB, ~QH of up/down counter 1 are all “H”.
Before reaching "i", the upper limit comparator 2 matches the set value from the microcomputer 6. Then, OR circuit 4
The output Z of the JK flip-flop 5 falls to "Low" by one pulse portion, and the output Q of the JK flip-flop 5 is inverted from "Low" to "Hi". And that signal is S of up/down counter 1
1 terminal, and the up/down counter 1 switches to a countdown state.

In the countdown state, the up/down counter 1 performs a countdown operation in accordance with the clock signal CLK. and output terminals QA, QB, ~QH
Before they all become "Low", the lower limit comparator 3 matches the set value from the microcomputer 6, the output Z of the OR circuit 4 becomes "Low" by one pulse, and the output Q of the JK flip-flop 5 becomes "Low". The signal is inverted from "Hi" to "Low" and the signal is input to the S1 terminal of the up/down counter 1, so that the up/down counter enters the count-up state again.

The carrier signal T thus created is input to the comparator 7 together with the reference sine wave signals A, B, and C, and the comparator 7 outputs a PWM wave signal. The duty ratio of this PWM wave signal at each point on the time axis changes according to the instantaneous value at each point of the reference sine wave signals A, B, and C, and the switching elements 39 to 44 are controlled by this PWM wave signal. By doing so, an alternating current voltage is generated between the current lines U, V, and W, and the three-phase motor 45 is operated.

FIG. 3 shows the current detection and current detection section of the inverter power supply device in this embodiment. 10 is motor 4
A current detection section 11 detects the magnitude of the current flowing through the motor 45 and sends the detection signal to the microcomputer 6; and a voltage detection section 11 detects the voltage applied to the motor 45 and sends the detection signal to the microcomputer 6. As the load increases, the output voltage drops, so in order to compensate for this, the output voltage is detected and input to the microcomputer 6, and the microcomputer 6 sets the upper limit comparator 2 and lower limit comparator 3 according to the procedure shown in FIG. Configured to toggle values. That is, if the load is normal and the output voltage is appropriate, the set values of both comparators are increased, and the amplitude of the carrier signal T is increased as shown by the broken line in FIG. 4(a). When it becomes necessary to increase the output voltage, the set values of both comparators are switched to lower values, and the amplitude of the carrier signal T is lowered as shown by the solid line in FIG. 4(a).

In this embodiment as well, the amplitudes of the reference sine wave signals A, B, and C are normally changed and the output voltage is adjusted so that the ratio between the motor torque and the frequency of the output AC voltage is always constant. Ru. In other words, when the output voltage is low, the amplitude of the reference sine wave signals A, B, and C is lowered, and when the output voltage needs to be increased, the amplitude of the reference sine wave signals A, B is lowered.
, C increase the amplitude. However, the reference sine wave signal A
, B, and C are determined by the power supply voltage (5V) of the D/A converter 7.
), so the reference sine wave signals A, B,
There is a limit to increasing the amplitude of C. Therefore, if the output voltage drops due to a large load, the set values of both comparators should be lowered according to the degree of drop, and the amplitude of the carrier signal T should be lowered as shown by the solid line in Figure 4(a). As shown in Figure 4(b), PW
A very long on time occurs in the M-wave signal, increasing the average voltage as shown by the dashed line M in FIG. 4(b). Figure 4 (
c) shows a PWM wave signal when the amplitude of the carrier signal remains high as shown by the broken line in FIG. 4(a). In this case, the average voltage remains low as indicated by the dashed line N in FIG. 4(c).

In the above embodiments, a triangular wave signal was used as the carrier signal, but it has a waveform that increases linearly, then decreases linearly with the same slope as the increase, and repeats this periodically. Any other waveform signal may be used as long as it is a signal, such as a trapezoidal wave signal. Further, in the above embodiment, the up/down counter 1 is configured to generate a carrier signal by repeating counting up and down, and the amplitude of the carrier signal is changed by rewriting the value set in the comparator. Since the configuration is such that switching between up and countdown is adopted, the amplitude of the carrier signal can be directly changed by the signal from the microcomputer. In other words, it is possible to change the amplitude of the carrier signal by directly setting the data output from the microcomputer to the comparator.

[0028]

As described above, the present invention provides a PWM wave signal generation section that generates a PWM wave signal whose pulse width changes in synchronization with the reference sine wave by comparing the carrier signal with the reference sine wave. In an inverter power supply device that has a pair of switching elements that switch complementary to each other using PWM waves, by providing a means to suppress the amplitude of the carrier signal according to the output current or output voltage, the carrier signal can be suppressed when a large load is applied. By keeping the amplitude of the signal small, it is possible to create a state in which the amplitude of the reference sine wave signal exceeds the amplitude of the carrier signal, and at that time, the ON time of the PWM wave signal can be lengthened, and the output voltage can be increased. It is possible to prevent a decrease in the motor drive torque by preventing a decrease in the motor drive torque.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a carrier signal generation circuit provided in an inverter power supply device according to an embodiment of the present invention.

[Figure 2
] Timing chart showing the operation of the carrier signal generation circuit in the same embodiment

[Fig. 3] A circuit diagram showing a current detection section and a voltage detection section of the inverter power supply device in the same embodiment.

[Fig. 4] Waveform diagram for explaining the operation of the inverter power supply device in the same embodiment.

FIG. 5 is a flowchart explaining the operation of the inverter power supply device in the same embodiment.

[Figure 6] Schematic configuration diagram of a conventional inverter power supply device

[Figure 7
] Timing chart to explain the operating principle of the inverter power supply

[Fig. 8] Timing chart for explaining the operating principle of the inverter power supply device

[Figure 9] Waveform diagram showing the operation of the inverter power supply device

[Figure 10] Waveform diagram showing the operation of the inverter power supply device

[Explanation of symbols]

1 Up/down counter 2 Upper limit comparator 3 Lower limit comparator 4 OR circuit 5 JK flip flop 7 D/A converter 8 Comparator

Claims (2)

[Claims] 1. A carrier generating means for generating a carrier signal that periodically increases and decreases in a linear manner, and a pulse width that is adjusted in synchronization with the reference sine wave signal by comparing the carrier signal and a reference sine wave signal. Changing PW
a PWM wave signal generation section that generates an M wave signal;
a switching section comprising a pair of switching elements that switch complementary to each other in response to a wave signal, and configured to supply a voltage at a connection point of the pair of switching elements to a load; An inverter power supply device comprising amplitude changing means for changing the amplitude. 2. The scope of the present invention is characterized in that the amplitude changing means is configured to change the amplitude of the carrier signal to be smaller than the amplitude of the reference sine wave signal when the load increases. The inverter power supply device according to item 1.