JPS642031B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention provides an inverter circuit having at least one pair of switching elements whose conduction is controlled alternately, a transformer whose primary winding is connected to a DC power source via this inverter circuit, and a secondary winding of this transformer. A rectifier connected to the switching element, a smoothing capacitor connected between the rectifier and the load, and a control means for maintaining the output voltage supplied to the load at a desired value by controlling the conduction rate of the switching element. Regarding switching regulators.

[Conventional technology]

Conventionally, series regulators have been widely used as DC stabilized power supply circuits due to their excellent stability and low output voltage ripple, but they have low efficiency and large power losses due to series transistors. It has its drawbacks. For this reason, today there is a tendency to use efficient switching regulators that control the DC voltage on and off and control the output voltage based on the ratio of the on time to the off time. Generally, as this type of switching regulator, for example, a current source switching regulator having a circuit configuration shown in FIG. 1 is known.
That is, the switching regulator shown in Fig. 1 includes an inverter circuit INV in which switching elements T _r1 to _{T r4} such as transistors are bridge-connected to a DC power source E, and a transformer T to the AC output terminal of this inverter circuit INV. A rectifier circuit REC in which rectifier elements D ₁ to _{D 4} such as diodes are connected via a bridge.
The DC output terminal side of the rectifier circuit REC is connected to a load L _d via an output filter consisting of a smoothing reactor L and a smoothing capacitor C.
is connected, detects the voltage applied to this load L _d side, and switches each switching element T _r1 to _{T r4} that constitutes the inverter circuit INV based on this voltage detection value and the voltage command direct from the voltage command device. The configuration is such that the conductivity is controlled to keep the output voltage to the load L _d constant. The circuit for controlling the conductivity can be composed of a voltage detector VD, a voltage command VC, a comparison amplifier A, and a conductivity regulator CR connected to the DC output side terminal of the rectifier circuit REC. In addition, on the primary winding side of the transformer T,
A capacitor C _P for preventing biased magnetism is connected.

[Problem to be solved by the invention]

In the conventional switching regulator configured in this way, for example, when the switching frequency is 20KHz, the resonance frequency of the output filters L and C is set to be about 2 times lower than the switching frequency in order to sufficiently reduce the output voltage ripple. Decreasing the order of magnitude to approx.
It is common to set it to 200Hz. Therefore, in order to avoid the resonance point set in this way, the response frequency of the constant voltage control system should be 100Hz or less, and the response delay time should be 5ms.
That's all. Therefore, if you want to improve the response speed, you can increase the switching frequency above 20KHz, but there is a limit due to increased switching loss, etc., so the transient response characteristics to disturbances such as sudden changes in load may not be as good as the series regulation. It has the disadvantage that it is inferior to Rator. Furthermore, in conventional switching regulators, due to variations in the characteristics of the switching elements T _r1 to _{T r4} , a slight DC component is generated in the primary winding of the transformer T, causing the transformer T to become biased. Since an excessive excitation current may flow and damage the switching elements T _r1 to _{T r4} , it is necessary to provide overcurrent prevention means such as a capacitor C _P for preventing biased magnetization, as shown in FIG. Furthermore, in conventional switching regulators, when obtaining an ultra-high output voltage, the transformer T
A large charge/discharge current flows due to the stray capacitance of the secondary winding of the switching element T _r1 ~
In order to cause a large inrush current to flow through T _r4 , it is necessary to use a special transformer that can set the stray capacitance to be extremely small. As mentioned above, conventional switching regulators have excellent characteristics in terms of efficiency, but they also have many drawbacks in terms of response characteristics and manufacturing, and they also have drawbacks such as extremely limited range of application. Ta. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a switching regulator that can significantly improve the response characteristics, which have been considered to be shortcomings of conventional switching regulators, and is easy to manufacture.

[Means to solve the problem]

In order to solve such problems, the present invention
The switching regulator of the type mentioned at the beginning includes a rectifier circuit to which a current related to the output current is supplied to limit the output current of the inverter, a reactor connected to the DC side of the rectifier circuit, and a reactor connected to the DC side of the rectifier circuit. another switching element that short-circuits the DC terminals of the rectifier circuit via the reactor; a switching means that connects the reactor to a DC power source in order to regenerate the energy stored in the reactor when the other switching element is turned off; and a reactor. The present invention is characterized by the provision of a current limiting circuit comprising a control circuit for controlling on/off of another switching element to maintain the current at a desired value.

【Example】

Next, embodiments of the switching regulator according to the present invention will be described in detail below with reference to the accompanying drawings. In the embodiment shown in FIG. 2, switching elements 10a to 10d made of transistors are
an inverter circuit 10 bridge-connected to the
It consists of a transformer 14 connected to the AC output side terminal of the inverter circuit 10, and a diode rectifier circuit 16 connected to the secondary winding side of the transformer 14. A load 20 is connected through an output filter consisting of a smoothing capacitor 18, and the input voltage of the load 20 is detected by a voltage detector 22. This detected voltage value is compared and amplified with a command value of a voltage command device 24 by an amplifier 26 to establish continuity. Inverter circuit 1 via rate regulator 28
The circuit is basically configured to adjust the conductivity of each of the switching elements 10a to 10d of 0 and to control the output voltage to the load 20 to be constant.
This basic circuit configuration is substantially the same as that of the conventional switching regulator shown in FIG. The circuit of this embodiment is characterized in that a current limiting circuit 30 is provided on the primary winding side of the transformer 14. That is, the current limiting circuit 30 connects the primary winding of the current transformer 32 to the AC output side terminal of the inverter circuit 10, connects the secondary winding of the transformer 32 to the diode bridge rectifier circuit 34, and A bridge rectifier circuit 34 is connected in parallel via a reactor 40 to a switching element 38 which is connected in series to the DC power supply 12 via a diode 36. Note that the switching element 38 is
On/off control is performed by a feedback control circuit comprising a current detector 42 that detects the current flowing through the diode bridge rectifier circuit 34, a current command device 44, and a conductivity regulator 46. Now, let the current supplied to the current limiting circuit 30 via the current transformer 32 and flowing through the diode bridge rectifier circuit 34 and the reactor 40 be _I30 . For convenience, this current I ₃₀ will be referred to as a reactor current. Therefore, when the switching element 38 is controlled to be on,
Diode bridge rectifier circuit 34, reactor 4
0 and the switching element 38 is formed, so that the reactor current I ₃₀ circulates in such a closed loop through the switching element 38. The reactor current I ₃₀ circulating in this closed loop is detected by a current detector 42 . Then, when this detection reactor current I ₃₀ exceeds the current limit value I ₃₀ * set by the current command device 44,
The switching element 38 is controlled by the conductivity regulator 46.
is controlled off. As a result, the closed loop is opened, so the reactor current I ₃₀ flows into the DC power supply 12 side through the diode 36, and the diode bridge rectifier circuit 34 → reactor 40 → diode 36 → DC power supply 12 → diode bridge rectifier It comes to circulate through a path called circuit 34. Thereby, the energy accumulated in the reactor 40 is regenerated to the DC power supply 12. Next, the operation of the switching regulator according to the present invention constructed as described above will be explained based on the operation waveform diagram shown in FIG. As is clear from the circuit configuration described above, the current limiting circuit 30 used in this embodiment is configured to regenerate energy generated for limiting the output current of the inverter circuit 10 to the DC power supply 12. First, the current limit value of the current limit circuit 30
I ₃₀ * is set as shown in FIG. Also,
The conductivity adjustment characteristic _e28 of the conductivity regulator 28 is set as shown in FIG.
If e ₂₆ becomes as shown in FIG. 3, each switching element 10a to
Output signal e _a of the conductivity regulator 28 for 10d
e _d becomes as shown in FIG. 3. As a result, the output voltage e 10 of the inverter circuit ₁₀ and the transformer 14
The primary current _I14 is as shown in FIGS. 4 and 5, respectively. Further, the secondary voltage e ₃₂ of the current transformer 32 in this case is as shown in FIG. 3, 7. In this way, the output current I ₁₈ and the output voltage e ₂₂ supplied to the load 20 side via the transformer 14 are respectively
As shown in FIGS. 6 and 8, the output voltage _e22 is controlled to be substantially constant. Next, the operation of regenerating energy to the DC power source will be explained in detail with reference to FIG. 4. When the switching element 38 is controlled to be off, as described above, a closed loop consisting of the diode bridge rectifier circuit 34, the reactor 40, and the switching element 38 is configured on the secondary side of the current transformer 32. , the reactor current I ₃₀ flowing in this closed loop increases due to the energy generated on the secondary side of the current transformer 32. This is illustrated in FIG. 4 between time points _t1 and _t2 . Specifically, the third
A voltage obtained by rectifying the secondary voltage e 32 of the current transformer ₃₂ shown in the figure by the diode bridge rectifier circuit 34 is applied to both ends of the reactor 40, and the reactor current
I ₃₀ will increase. This reactor current
I ₃₀ does not change suddenly because the reactor 40 is included in the closed loop. The conduction sections of the inverter circuit 10 are indicated by a, b, c, and d in FIG.
I ₁₄ and reactor current I ₃₀ can only flow at values determined by the current transformation ratio of current transformer 32. That is, the primary current I ₁₄ of the transformer 14 is clamped to the reactor current I ₃₀ . This is the basis of the current limiting operation in the present invention. (However, if the current transformation ratio of the current transformer 32 is set to 1, it is essentially the same as if the current transformer 32 does not exist, so of course the current transformer may be omitted. ) In Figure 4,
Shaded portions A, B, C, and D of the reactor current I ₃₀ determine the peak value of the primary current I ₁₄ of the transformer 14. When this reactor current I ₃₀ exceeds the current limit value I ₃₀ * set by the current command device 44,
The switching element 38 is controlled by the conductivity regulator 46.
is controlled off at time t ₂ . Then, as mentioned above, the reactor current I ₃₀ flows through the switching element 38.
The current is commutated from to the diode 36. All of the reactor current I ₃₀ at this time flows into the DC power supply 12, and the energy of the reactor 40 is regenerated to the DC power supply 12. During this period t ₂ to _{t 3} , the power supply voltage is higher than the voltage obtained by rectifying the secondary voltage e ₃₂ of the current transformer 32 by the diode bridge rectifier circuit 34, so the reactor voltage I ₃₀ decreases. At time _t3 , the reactor current _I30 reaches the current limit value set by the current command device 44.
When I ₃₀ * is lower than I 30 *, the switching element 38 is turned on again by the conductivity regulator 46 . By repeating this process, the primary current I ₁₄ of the transformer 14 is restricted smoothly and efficiently, and the energy of the reactor 40 is regenerated into the power source. In FIG. 4, the on-off period of the switching element 38 is shown to be sufficiently longer than the switching period of the inverter circuit 10, but since the on-off period of the switching element 38 can be selected independently of the inverter circuit 10, Inverter circuit 1
There is no problem even if the switching period is shorter than 0. Note that the diode 36 is a switching element 38.
When the switching element 38 is in the on state, it is non-conducting, and when the switching element 38 is in the off state, it is conducting and leads the reactor current I ₃₀ to the DC power supply 12.
Therefore, instead of the diode 36, for example, a transistor is connected, and the switching element 3
The switching element 38 and the transistor are controlled by the conductivity regulator 46 so that when the switching element 8 is on, the transistor is turned off, and when the switching element 38 is off, the transistor is turned on. It can be easily understood from the above-mentioned operation mode of the present invention that this may be done. Furthermore, in this example circuit, the output voltage
It was confirmed that the response frequency for controlling e ₂₂ to be constant is approximately the same according to automatic control theory and experimental results, and the switching frequency is = 1/T (Hz) [see Fig. 3, 5]. Also, the response delay time is r≒
It was also confirmed that T/2 (sec) [see FIG. 3, 6]. That is, switching frequency = 20K
If it is set to Hz, the response frequency will also be 20KHz, and the response delay time in this case will be approximately 25μs.

【Effect of the invention】

As can be fully understood from the description of the embodiments described above, the switching regulator according to the present invention can limit the output current of the inverter circuit, and also reduce the energy generated to limit the output current of the inverter circuit. can be regenerated into DC power and used effectively. Furthermore, according to the present invention, it is possible to omit the installation of a smoothing reactor that was conventionally required as an output filter, and moreover, it is possible to improve transient response speed by approximately 200 times compared to a conventional switching regulator. It became possible. In other words, the response frequency can be improved from 100Hz to 20KHz,
Response delay time can be improved from 5ms to 25μs. In addition, by providing a current limiting circuit, it is possible to limit overcurrent when unbalanced magnetization occurs in the transformer.
There is an advantage that there is no need for a bias prevention means for the transformer as in the conventional case. Note that it is necessary to provide a bias prevention means to the current transformer constituting the current limiting circuit. Furthermore, it is very advantageous for the stray capacitance of transformer windings, making it easy to realize ultra-high voltage DC stabilized power supply circuits, and in particular, since it is transformer-coupled, radar power supplies, etc. It can be suitably applied as a high-voltage, high-precision DC stabilized power supply circuit. Although the preferred embodiments of the present invention have been described above, it goes without saying that various design changes can be made without departing from the spirit of the present invention.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a conventional switching regulator, Fig. 2 is a circuit diagram showing an embodiment of a switching regulator according to the present invention, and Figs. 3 and 4 are respectively shown in Fig. 2. FIG. 3 is a waveform chart for explaining the operation of the circuit shown in FIG. 10... Inverter circuit, 10a to 10d... Switching element, 12... DC power supply, 14... Transformer,
16...Diode rectifier circuit, 18...Smoothing capacitor, 20...Load, 22...Voltage detector, 24...Voltage command device, 26...Amplifier, 28...Conductivity regulator, 3
0... Current limiting circuit, 32... Current transformer, 34... Diode bridge rectifier circuit, 36... Diode, 38
...Switching element, 40...Reactor, 42...
Current detector, 44...Current command device, 46...Conductivity regulator.

Claims (1)

[Claims] 1. An inverter circuit 10 having at least one pair of switching elements whose conduction is controlled alternately; a transformer 14 whose primary winding is connected to a DC power source via this inverter circuit; Rectifier 16 connected to the secondary winding
and a smoothing capacitor 18 connected between the rectifier and the load 20, and a control means 28 for maintaining the output voltage supplied to the load at a desired value by controlling the conduction rate of the switching element. The switching regulator includes a rectifier circuit 34 to which a current related to the output current is supplied to limit the output current of the inverter, a reactor 40 connected to the DC side of the rectifier circuit, and a reactor 40 connected to the DC side of the rectifier circuit. another switching element 38 for short-circuiting the DC terminals of the rectifier circuit through the switching element; and circuit means 36 for connecting the reactor to a DC power source in order to regenerate the energy stored in the reactor when the other switching element is off. A switching regulator comprising: a control circuit 46 that controls on/off the other switching element to maintain the current of the reactor at a desired value; and a current limiting circuit 30.