JPH09261963A - Converter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the step-up/step-down of a voltage with a small loss by a switching device having a low withstand voltage. SOLUTION: A switching device 1, a reactor 4, a switching device 5, a diode 2 and the anode of a diode 3 are connected to a rectification circuit 6. A load 50 is connected between the cathode of the diode 3 and the minus side of the rectification circuit 6. A rectification circuit voltage waveform Vrip, a rectification circuit current waveform Irip and a voltage between both the ends of the load 50 are inputted to a control circuit 40 which controls so as to have the voltage between both the ends of the load 50 equal to an output voltage Vref and to have the current waveform Irip similar to the voltage waveform Vrip. If a voltage drop when the switching device is in a ON-state is denoted by Vce1 and a voltage drop when the diode 3 is in an ON-state is denoted by VF2, when the relation between the voltage value Vrip and the voltage value Vref is: Vrip>Vref+Vce1+VF2, the device 5 is turned off and the device 1 is subjected to the pulse width modulation control to perform a step-down type operation and, when the relation between the voltage value Vrip and the voltage value Vref is: Vrip<Vref+Vce1, the device 1 is turned on and the device 1 is subjected to the pulse width modulation control to perform a step-up type operation. When the relation between the voltage value Vrip and the voltage value Vref is:Vref+Vce1<Vrip<Vref+Vce1+VF2, both devices 1 and 5 are subjected to the pulse width modulation control to perform a step-up/ step-down type operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a converter circuit in which a current waveform from a single-phase AC power supply has the same waveform as a voltage waveform and a power supply power factor is 1.

[0002]

2. Description of the Related Art In recent years, there has been a demand for a countermeasure against generation of a power supply harmonic current in an AC power supply device, and as a method therefor, a circuit using a boost converter has been proposed. The method using the boost converter simultaneously controls the output voltage to be constant while controlling the current waveform to match the rectified pulsating voltage waveform. In order to satisfy this condition, the output voltage becomes higher than the pulsating current voltage.For example, in a device that drives a motor based on an AC power source, the DC conversion circuit by this boost converter and the obtained DC drive the motor The motor is driven at a variable speed by a so-called inverter circuit that creates an alternating current for use.

FIG. 4 shows an example of the circuit. In FIG.
The voltage Vrip, which has a pulsating waveform due to passing through the rectifying diode bridge 6 from the AC power supply 7, is input to the power supply harmonic control means 63 by the voltage detection means 9. The positive side of the pulsating current voltage is connected to the reactor 4, and the other end of the reactor 4 is connected to the anode terminal of the diode 3 and the switching element 5. The other end of the switching element 5 is connected to the negative side of the rectifying diode bridge 6. The cathode of the diode 3 is the capacitor 1
2 is connected to the positive side of the three-phase switching element group 100 and the negative side of the capacitor 12 and the three-phase switching element group 100 is connected to the negative side of the rectifying diode bridge 6. Current sensor 10
Detects the current Irip between the switching element 5 and the rectifying diode bridge 6 and inputs it to the power supply harmonic control means 63. Similarly, the voltage detecting means 58 causes the capacitor 1
The voltage of 2 is detected and input to the power supply harmonic control means 63.

The operating principle of the power supply harmonic control means 63 will be described. In the power supply harmonic control means 63, the current Irip
The waveform of is controlled to have the same shape as the ripple voltage Vrip,
In addition, the current I is adjusted so that the voltage Vdc of the DC part becomes a predetermined value.
Adjust and control the size of rip. That is, an error between the predetermined DC voltage and the current DC voltage Vdc is obtained, and the amplitude of the waveform of the pulsating current voltage Vrip is adjusted based on the error. An error between the adjusted pulsating current voltage and the current waveform Irip is obtained, the error is pulse-width modulated, and the switching element 5 is turned ON / OF.
Perform F control. When the switching element 5 is ON, current is accumulated in the reactor 4 and the switching element 5 is OFF.
Then, the current accumulated in the reactor 4 charges the capacitor 12 via the diode 3.

Next, the motor drive circuit portion in the subsequent stage will be briefly described. A so-called DC brushless motor 14 using a permanent magnet as a rotor is connected to the output of the three-phase switching element 100, and a DC voltage is distributed in three phases according to the rotation phase of the rotor to drive the motor 14 at a variable speed. . More specific driving method of the DC brushless motor 14 is described in pages 241 to 242 of "Introduction to Power Electronics" by Yamamura and Ohno.

[0006]

However, when the rotation speed of the motor 14 is low, it is appropriate to apply a low voltage to the motor 14, but according to the configuration described in FIG. 4, the DC voltage Vdc It is difficult to make the voltage low. That is, the power supply harmonic control operation needs to be a voltage in which the DC voltage Vdc is higher than the input voltage Vrip. If the DC voltage Vdc is lower, a current will flow through the reactor 4 and the diode 3 regardless of whether the switching element 5 is ON or OFF, and it is impossible to make the voltage lower than Vrip. The reason is that it cannot be controlled.

Therefore, in order to drive the motor 14 with a low applied voltage, the three-phase distribution control means 62 causes the three-phase bridge type switching element group 100 to undergo pulse width modulation.
Therefore, it is necessary to control so that the average value of the motor applied voltage becomes a voltage smaller than the DC voltage Vdc.

However, when the motor 14 is driven by the pulse width modulation, there is a problem that the current fluctuation of the remaining pulse width modulation component causes a decrease in the efficiency of the motor 14 and the generation of electromagnetic noise. Further, there is also a problem that a part of the current fluctuation of the pulse width modulation component leaks through the electrostatic capacitance in the air gap of the motor 14, causing a noise current to flow to the ground.

Another method is to connect a step-down converter to the output of the step-up converter and selectively switch the three-phase bridge type switching element group with the output voltage. Two of them are connected in series, two reactors or the like are required, and there is a problem that the loss of the converter is doubled.

As another method, there is a method of stepping up and down by using a negative output type converter, but the polarities of the input voltage and the output voltage are different, and the withstand voltage required for the switching element is increased. There is a problem.

In consideration of the above problems of the conventional method, the present invention can realize a converter circuit with a small dynamic switching loss only by a switching element having a low breakdown voltage.

[0012]

According to the present invention, both positive and negative output terminals of a rectifier circuit are connected from a positive side to a negative side by a first switching element, a reactor and a second switching element. The output terminal of the first switching element and the negative output terminal of the rectifier circuit are connected by a first diode in the direction opposite to the polarity of the rectifier circuit, and between the reactor and the second switching element. The anode of the second diode is connected between
A load is connected between the cathode of the second diode and the negative output terminal of the rectifier circuit, and the output voltage waveform Vrip of the rectifier circuit and the output current waveform Iri of the rectifier circuit are connected.
By inputting p and the voltage across the load, the voltage across the load is equal to the voltage Vref to be output, and the output current waveform Irip of the rectifier circuit is similar to the output voltage waveform Vrip of the rectifier circuit. A converter circuit provided with a control circuit for controlling the output voltage of the rectifier circuit, wherein the rectifier circuit output voltage Vrip and the voltage value Vref to be output have a voltage drop when the first switching element is turned on. Let Vce1 be the voltage drop when the second diode is on and VF2

[0013]

[Formula 1] When Vrip> Vref + Vce1 + VF2, the second switching element is turned off and the first switching element is subjected to pulse width modulation control,
The voltage across the load is equal to the voltage Vref to be output,
Moreover, the output current waveform Irip of the rectifier circuit is controlled so as to be similar to the rectifier circuit output voltage waveform Vrip, and the relationship between the rectifier circuit output voltage Vrip and the voltage value Vref to be output is:

[0014]

## EQU00002 ## When Vrip <Vref + Vce1, the first switching element is turned on.
Then, the pulse width modulation of the second switching element is performed, the voltage across the load is equal to the voltage Vref to be output, and the output current waveform Irip of the rectifier circuit is the output voltage waveform Vr of the rectifier circuit.
The output voltage V of the rectifier circuit is controlled so as to be similar to ip.
The relationship with the voltage value Vref that rip should output is

[0015]

[Expression 3] Vref + Vce1 <Vrip <Vref +
When Vce1 + VF2, the first switching element and the second switching element are pulse-width modulated at the same time so that the voltage across the load is equal to the voltage Vref to be output, and the output current waveform Irip of the rectifier circuit. Is the rectifier circuit output voltage waveform Vrip
It is characterized by controlling so as to be similar to. As a result, when the input voltage is lower than the voltage to be output, the converter is a step-up converter, when the input voltage is high, the converter is a step-down converter, and when the input voltage is about the same, the converter is a buck-boost converter. Also in this case, the input current waveform control and the output voltage control are performed.

Further, by providing a means for performing the switching of the above-mentioned 3 control in synchronism with the pulse for pulse width modulation, it is possible to prevent the pulse intervals at the time of switching from becoming irregular.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a circuit block diagram showing a configuration of an embodiment of the present invention, and particularly a circuit diagram showing a main circuit portion.
The configuration will be described below together with the operation. The output from the AC power supply 7 becomes a pulsating voltage waveform Vrip through the rectifier circuit 6 by the diode bridge. First on the positive output of the rectifier circuit 6
Of the first diode 2 and the reactor 4 are connected to the tip of the first switching element 1, and the anode of the first diode 2 is connected to the negative side of the rectifier circuit 6. There is. On the other hand, the other side of the reactor 4 is connected to the anodes of the second switching element 5 and the second diode 3, and the other end of the second switching element 5 is connected to the minus side of the rectifier circuit 6. The cathode side of the second diode 3 is connected to the plus side of the load 50, and the minus side of the load 50 is connected to the minus side of the rectifier circuit 6. Load 50
For example, the motor drive circuit shown in the conventional example is possible.

Next, regarding the signal flow of the control system, the output voltage Vrip of the rectifier circuit 6 is divided by the resistors 141 and 142 and input to the control circuit 40. The current Irip in the rectifier circuit 6 is input to the control circuit 40 by the current sensor 10, and the output voltage VDC on the load 50 side is the resistance 14
The voltage is divided by 3, 144 and input to the control circuit 40. The control circuit 40 controls the switching elements 1 and 5 based on the above input information and the voltage Vref to be output. The reason why the voltage detection part is divided is that the voltage level handled by the control circuit 40 and the voltage level of the main circuit part are adjusted, and if the circuit with high withstand voltage is adopted inside the control circuit 40, it will be divided. It goes without saying that you can enter without entering.

FIG. 3 is a concrete circuit diagram of the inside of the control circuit 40. The comparison means 31 compares the voltage Vref to be output with the output voltage Vdc, and sends the result to the compensation means 32.
In the compensating means 32, the comparison error is subjected to control compensation calculation such as proportional integration calculation and the result is sent to the multiplier 33. The multiplier 33 multiplies the pulsating current voltage Vrip by the information based on the comparison error, and sends the result to the comparison means 34. The comparison means 34 compares it with the pulsating current Irip and compares the result with the compensation means 3
Send to 5, 36, 37. The compensating means 35, 36, 37 perform control compensation calculation on the comparison error by proportional-plus-integral calculation or the like, and send the result to the comparing means 38, 39, 40. The comparing means 38, 39, 40 compare the output of the oscillating means 41, and send the result via the selecting circuits 42, 43 to the switching elements 1, 5 as a switching command to perform the switching operation. The selection circuit 42 has an ON fixed command 44
And the output of the comparing means 40 or the output of the comparing means 38, and the selecting circuit 43 selects any of the output of the comparing means 39, the output of the comparing means 40, and the OFF fixed command 45. . These commands are given by the D flip-flop groups 53a, 53b, 53c. The D flip-flop groups 53a, 53b, and 53c synchronize the outputs of the digital comparator 47, the NOR circuit 46, and the digital comparator 48 with the output of the oscillating means 41. The digital comparator 47 has a value obtained by adding the voltage drop Vce1 when the first switching element 1 is ON to the voltage Vref to be output,
The magnitude of the pulsating current voltage Vrip is compared, and the digital comparator 48 compares the voltage Vref to be output with the voltage drop Vce1 when the first switching element 1 is ON and the voltage drop Vce1 when the second diode 3 is ON. The magnitude of the pulsating current voltage value Vrip is compared with the value obtained by adding the voltage drop amount VF2, and the comparison polarity is opposite to that of the first digital comparator 47.

Considering the circuit configuration of FIG. 3 largely, the comparison means 3
It can be said that the pulse width modulation means and the control circuit are constituted by 8, 39, 40 and the oscillation means 41. By controlling the pulse width modulation of the switching elements 1 and 5 by comparing the output of the multiplier via the pulsating current voltage Vrip with the current Irip, a control system with the same current waveform and voltage waveform is configured, and it corresponds to the load. The control system that adjusts the amount of power supply current by DC voltage Vdc
The pulse width modulation control is performed on the switching elements 1 and 5 via the comparison means 31 and the compensation means 32. In particular, when the input voltage Vrip is lower than the voltage Vref to be output next, the first switching element 1
Is turned on and a pulse width modulation is performed by the second switching element 5 to form a boost converter. When the input voltage is high, the second switching element 5 is turned off and the pulse width is changed by the first switching element 1. By performing the modulation, it becomes a step-down converter, and when it is about the same, it becomes a step-up / down converter in which two switching elements are simultaneously turned on / off.

The compensating means 35, 36 and 37 are provided exclusively for the following reasons. In the case of a step-down converter, it is necessary to lengthen the ON period in order to increase the output current or output voltage, and in the case of a step-up or step-up / down converter, when increasing the output,
It is necessary to lengthen the OFF period. This is because the polarities of the switching elements to be controlled are opposite and the operating points are different.

As described in the conventional example, when the brushless motor is driven as a load, the voltage Vref to be output changes depending on the difference from the rotation speed to be output.
That is, a means for comparing the number of revolutions to be output before inputting Vref with the actual number of revolutions is added.

Next, the operating principle of the present invention will be described on the time axis with reference to FIG. "Vref + Vce1" including circuit loss
Therefore, when “Vrip” is low, that is, at time t1
Before this, the first switching element 1 is always in the ON state, and the second switching element 5, the reactor 4,
The second diode 3 serves as a boost converter.
This is because the boosting operation is performed by the voltage obtained by subtracting the voltage drop of the first switching element 1 which is turned on.

Next, as in the period from time t2 to t2, "V
If "Vrip" is higher than "ref + VF2 + Vce1",
The second switching element 5 is in the OFF state, and the first switching element 1, the first diode 2, and the reactor 4 serve as a step-down converter. This is due to the maximum value of the voltage that can be output by the step-down converter when the current flows through the second diode 2 to the load side and the loss of the first switching element 1 is also taken into consideration.

Finally, between times t1 and t2, or t3 and t4.
In the meantime, when the voltage is an intermediate voltage such as between t5 and t6, the step-up / down converter is achieved by simultaneously turning ON / OFF the first switching element 1 and the second switching element 5. In this period, since the voltage range in which neither the step-up operation nor the step-down operation described above can be operated is performed, the step-up / step-down converter cannot be used for operation. In either case, the input current waveform control and the output voltage control are performed.

Since the loss voltage of the diode is generally smaller than the output voltage VDC, from FIG. 1, any one of the step-up type, step-down type, and step-up / down type is selected in all periods including the voltage drop of the switching element. It is possible to realize the converter in time division. Also, it can be seen that there is almost one element that dynamically switches, and the dynamic switching loss is small. Further, in each period, the converter is a step-up type, step-down type, or step-up / down type converter, and the withstand voltage of the switching element may have individual performance, and only one reactor is required, and the configuration is simple.

[0028]

As is apparent from the above description,
The present invention performs the step-up operation, the step-down operation, and the step-up / step-down operation in a time-sharing manner, so that only the switching element with low withstand voltage
A converter circuit with less dynamic switching loss can be realized.

[Brief description of drawings]

FIG. 1 is a timing waveform chart showing the operating principle of an embodiment of the present invention.

FIG. 2 is a block diagram of a main circuit according to the above embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a power source harmonic control unit in the above embodiment.

FIG. 4 is a circuit block diagram of a conventional example.

[Explanation of symbols]

 1 1st switching element 2 1st diode 3 2nd diode 4 reactor 5 2nd switching element 6 Rectifier circuit 40 Control circuit

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yoshiteru Ito 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. The positive and negative output terminals of the rectifier circuit are connected from the positive side to the negative side by a first switching element, a reactor and a second switching element,
An output terminal of the first switching element and a negative output terminal of the rectifier circuit are connected by a first diode in a direction opposite to the polarity of the rectifier circuit, and between the reactor and the second switching element. Is connected to the anode of the second diode, a load is connected between the cathode of the second diode and the negative output terminal of the rectifier circuit, the output voltage waveform Vrip of the rectifier circuit, and the rectifier circuit. Input current waveform Irip of the load and the voltage across the load, the voltage across the load is equal to the voltage Vref to be output, and the output current waveform Ir of the rectifier circuit
A converter circuit provided with a control circuit for controlling ip to be similar to the rectifier circuit output voltage waveform Vrip, wherein the control circuit has a relationship between the rectifier circuit output voltage Vrip and a voltage value Vref to be output. Where Vce1 is the voltage drop when the first switching element is on and VF2 is the voltage drop when the second diode is on, and when Vrip> Vref + Vce1 + VF2 The switching element of is turned off, the first switching element is subjected to pulse width modulation control,
The voltage across the load is equal to the voltage Vref to be output,
In addition, the output current waveform Irip of the rectifier circuit is controlled so as to be similar to the rectifier circuit output voltage waveform Vrip, and the relationship between the rectifier circuit output voltage Vrip and the voltage value Vref to be output is as follows: Vrip <Vref If + Vce1, turn on the first switching element
Then, the pulse width modulation of the second switching element is performed, the voltage across the load is equal to the voltage Vref to be output, and the output current waveform Irip of the rectifier circuit is the output voltage waveform Vr of the rectifier circuit.
It is controlled to be similar to ip, and the relationship between the rectifier circuit output voltage Vrip and the voltage value Vref to be output is as follows: Vref + Vce1 <Vrip <Vref +
When Vce1 + VF2, the first switching element and the second switching element are pulse-width modulated at the same time so that the voltage across the load is equal to the voltage Vref to be output, and the output current waveform Irip of the rectifier circuit. Is the rectifier circuit output voltage waveform Vrip
A converter circuit characterized by controlling so as to be similar to. 2. The switching of the control system in the three cases,
The converter circuit according to claim 1, wherein the pulse width modulation is performed in synchronization with the output of the oscillating means.