JPH0470878B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of controlling a bidirectional forward conversion device used in an inverter, particularly an inverter for driving a motor.

[Conventional technology]

When driving an induction motor or synchronous motor (particularly a permanent magnet rotor for a servo) with an inverter, in braking (regeneration) mode, rotational energy is regenerated and the capacitor in the DC link is charged. If this is left unattended, the capacitor voltage will continue to rise and become overvoltage, eventually leading to destruction. To prevent overvoltage, two methods have traditionally been used: (a) resistance discharge method and (b) power regeneration method, but for equipment that requires frequent braking or equipment with large capacity, it is recommended to use methods such as high efficiency and energy saving. The latter b power regeneration type is the mainstream.

In the case of a power regeneration type, a bidirectional forward conversion device having a rectification function in both directions of power running and regeneration is used as the forward conversion device. Some bidirectional forward conversion devices have thyristor bridges connected in reverse parallel, but this requires wasted time during switching to prevent short circuits between the power running/regeneration bridges, and involves frequent power running and regeneration operations. It has poor response characteristics and is unsuitable for driving electric motors.

In addition, with recent advances in PWM control technology, it is now possible to control both frequency and voltage in the inverse conversion section.
The DC voltage of the DC link portion may be fixed, and the powering direction forward conversion device no longer requires a controllable function.

That is, as a bidirectional forward conversion device, conversion in the power running direction is performed by a simple rectifier bridge without a controllable function, and conversion in the regeneration direction is performed using a self-extinguishing switch element, making it possible to adjust the regenerative energy. A regeneration bridge is used.

By the way, the common method of controlling a regenerative bridge is to use the AC power supply voltage as phase information and perform sine wave PWM control or phase shift control, but this requires voltage and current control loops, and the circuit The structure was complicated.

[Problem that the invention seeks to solve]

The present invention aims to simplify the control circuit of the regenerative bridge and improve its control performance in a bidirectional forward conversion device comprising a rectifier bridge and a regenerative bridge requiring a self-extinguishing switch element such as a transistor.

[Means for solving problems]

As the current command for the sine wave PWM control system that controls the regenerative current, we use a sine waveform synchronized with the AC power supply phase voltage whose amplitude is converted to the maximum value determined by the current capacity of the element, and This current deviation is amplified and PI adjusted to create a sine wave control signal, which is compared with the carrier signal and converted to a sine wave PWM signal, which is then continued in the same way as the resistive discharge type. It is characterized by

[Effect]

Considering that sine wave PWM control is to output the command sine wave faithfully as it is,
Performing sine wave PWM control on the regenerative bridge and using a sine wave with a power factor of 1 synchronized with the AC power supply phase voltage as the current command eliminates the need for any special processing or operation in the subsequent circuits, resulting in an extremely simple circuit. It is clear that this technology also facilitates control.

〔Example〕

FIG. 1 shows a block diagram of the embodiment, and FIG. 2 shows a time chart. In FIG. 1, 1 is a rectifier bridge, 2 is a regeneration bridge, and 3 is a DC link capacitor, which constitutes a bidirectional forward conversion device that allows current to flow in both directions of power running and regeneration. In the control circuit, 4 is a phase voltage detector of the AC power supply, 5 is a current detector, and 6 is a sine wave current command.The control circuit amplifies the deviation between the phase voltage of the voltage detector 4 and the regenerative current of the current detector 5. and PI
a current regulator for regulating and converting into a sinusoidal control signal, 7
is a triangular wave oscillator that generates a PWM carrier triangular wave, 8 is the first comparator that converts the sine wave control signal to a PWM signal, 9 is an insulation detector for detecting the DC link voltage, and 10 is the DC link capacitor tolerance. A second comparator that determines the magnitude relationship between the maximum voltage Ed-MAX and the DC link voltage Ed of the insulation detector output, 11 is the sine wave of the first and second comparators 8 and 10
An AND gate 12 superimposes a PWM signal and an overvoltage signal, and an isolation amplifier 12 converts the output of the AND gate 11 into a base signal of a regenerative bridge transistor.

In other words, the amplitude of the sinusoidal current command synchronized with the phase voltage is set to the maximum value determined by the current capacity of the element, and the deviation from the detected regenerative current is taken, resulting in a sinusoidal current deviation signal. Current amplification/
After being amplified and PI-adjusted through the regulator 6 and converted into a sine wave control signal, it is compared with a carrier triangular wave and converted into a sine wave PWM signal. This sine wave PWM signal waveform is such that when the magnitude relationship between the maximum allowable voltage Ed-MAX of the DC link capacitor and the detection voltage Ed is Ed-MAX≦Ed, the AND gate 11 is in an open state and is used for regeneration as it is. Used as base input of bridge transistor.
That is, a current with a power factor of -1 flows through the line, suppressing a rise in the capacitor voltage, and regenerating the motor rotational energy to the power supply side. Also, conversely, Ed−
When MAX>Ed, the circuit is closed to the AND gate 11, there is no output from the isolation amplifier 12, and the regeneration bridge 2 does not operate.

As mentioned earlier, the regenerative current command synchronized with the AC power supply phase voltage sets its amplitude to the maximum value of the element capacitance, and of course it is larger than the pre-conceived motor regenerative power amount. The maximum allowable capacitor voltage Ed−
The operation and stop of the regenerative bridge can be controlled based on the magnitude relationship between MAX and the detected voltage Ed. In other words, when Ed−MAX<Ed, the regenerative current is regenerated at the maximum current, and the capacitor voltage
Ed is the maximum voltage Ed− without passing the time shown on the left.
When the voltage drops below MAX, the regeneration bridge 2 automatically stops operating, and during this stop, energy is regenerated from the motor and the capacitor voltage rises, but if the capacitor voltage Ed reaches the maximum voltage Ed-MAX. For example, the regeneration bridge 2 generates a sine wave again.
It receives PWM signals and performs regenerative operation. The role of a limiting resistor in the so-called resistance discharge type is performed by a sinusoidal waveform current command synchronized with the phase voltage, and the switch element is replaced with a regeneration bridge transistor.

The time chart in Figure 2 shows the operating waveforms of each part, and in order from the top, the regenerative current command a of the AC power supply phase voltage, the regenerative current b, the sine wave control signal c of the current regulator 6 output, the carrier triangular waveform d, and the sine wave. The wave PWM signal e, the maximum allowable voltage signal Ed-MAX, the capacitor voltage Ed, and the regeneration bridge 2 base input signal f, and when Ed-MAX<Ed, the sine wave PWM signal e is directly sent to the regeneration bridge 2. On the other hand, when Ed−MAX>Ed, regeneration bridge 2
The base input of is cut off.

〔Effect of the invention〕

When a sine wave PWM method that faithfully outputs a command sine wave is used for regenerative current control, there is nothing special about using the sine waveform of the AC power supply phase voltage as phase information and directly using it as the sine wave current command. This eliminates the need for processing and operations, greatly contributing to circuit simplification and improved control performance.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the embodiment, and FIG. 2 is a time chart for explaining its operation. 1... Rectifier bridge, 2... Regeneration bridge, 3... Capacitor, 4... Phase voltage detector, 5
...Current detector, 6...Current regulator, 7...Carrier signal generator, 8...First comparator, 10...
Second comparator, 11...AND gate.

Claims (1)

[Claims] 1 In a bidirectional forward conversion device consisting of a rectifier bridge, an anti-parallel connected regenerative self-extinguishing element bridge, and a smoothing capacitor, the AC power source is used as the current command for the sine wave PWM control system that controls the regenerative current. A sinusoidal waveform synchronized with the phase voltage whose amplitude is converted to the maximum value determined by the current capacity of the element is used, the deviation is taken from the detected regenerative current, the current deviation is amplified, and the PI Adjust the sine wave control signal and compare it with the carrier signal.
Convert it to a PWM signal and compare the preset allowable DC voltage maximum value with the detected capacitor voltage. If the capacitor voltage is large, the above sine wave PWM signal is used as the bridge control signal for regeneration, and if the capacitor voltage is small, this signal is used as the bridge control signal for regeneration. A method for controlling a bidirectional forward conversion device, characterized in that a bridge control signal for regeneration is cut off.