Control system block schematic drawing like chart 2 shows.

The control function realizes by 51 monolithic integrated circuits, its function includes:
1. produces 250 ~ 1000HZ driving signal, controls 8 IGBT tube to have the foreword to lead passes, produces the square-wave voltage in the out-port which the pulse width may move.
2. uses the pulse-duration modulation the method realization output voltage continuously to be possible to move. Output wave shape like chart 3 shows.

3. examinations and demonstration function
After the prototype develops successfully, is good in the oil field movement, but another question appears suddenly, as a result of the working conditions and the condition reason, this power source out-port common the danger which short-circuits, also set the new request for this user: "The equipment did not fear short-circuits", user request reasonable, "under the rated voltage did not fear short-circuits" the request protection circuit fast and is effective.
Fast short-circuits the protection circuit
The general protection plan shuts off all IGBT tube. But to above 600v power source because the short-circuit current rise too is quick, shut off the signal also function, the IGBT tube already is burn outt. Must want to guarantee the IGBT tube to be safe and sound, must moreover take the measure. This article mentality is in the out-port series suitable inductance, reduces the short-circuit current with the inductance the ascending velocity, strives for the time to let IGBT the electric current in arrives in front of the limit value, the pipe can with enough time shut off. But after introduction inductance, as a result of huge di/dt, also can induce the peak voltage, this peak voltage can pose the huge threat to IGBT.
In order to guarantee short-circuits the protection unreliability, this article has taken the following measure:
1. installs the peak blanker (TVTE1. 5KE400CA). This component principle of work with 稳压管almost, when the voltage is lower than the breakdown voltage, in the tube does not have the electric current, needlessly consumes the energy. When the voltage is higher than the breakdown voltage, the pipe penetrates, gets up the clamping action. Because the pipe pressure resistance is insufficient, after passes through the suitable series, parallel to in contravariant bridge about generatrix. This may guarantee the generatrix voltage ±E on cannot appear endangers the IGBT security the peak voltage.
2. limits in the out-port series flows the inductance, this inductance function is prevents di/dt oversized before, in order to avoid IGBT is completely shut off the electric current surpasses the limit value. Below is the inductance quantity computation:
In the IGBT handbook nominal current is I0=150A
This power source fixed output current is IL=65A
In the IGBT handbook produces biggest pulse electric current for fixed 2 times
IMAX = 2* I0 =2*150=300A
About between the generatrix voltage is 2E �?1140*1.4 �?1600V
Usually allows 2E to have 20% undulation, therefore
EMAX=1.2*2E �?2000V
After short-circuits occurs, examines signal request severance approximately 2 mu s;
Branch instruction approximately 2 mu s;
Shuts off the signal the production and transmission approximately 2 mu s;
Shuts off on signal in IGBT electronics grid establishment time approximately 2 mu s.
Amounts to approximately 8 mu s, observed on IGBT with the oscilloscope to shut off the signal indeed compared to short-circuit occurs the time to retard about 8 mu s, above this proof analysis was correct. Has this section of detention main reason is 51 monolithic integrated circuits speeds slow, the action cycle is long. Based on the above estimate and actual is the basis, shuts off the signal the establishment time is
Delta t=8 mu s
The electric current rose in Delta t this period of time from IS, therefore maximum current rate of change di/dt was:
Di/dt = (IMAX --- IX)/Delta t= (300 - 117) /8 �?23 (A/ mu s)
Limits flows the inductance value to be supposed to be:
L=EMAX/ (di/dt) =2000/23 �?90 (mu H)
This inductance actually circles the system value control between 90--120 mu H. In order to reduce in the inductance the power loss, this inductance should be as far as possible small in the guarantee security situation. Its ferrite core should remain has the air gap, must guarantee in under the big pulse electric current function cannot be saturated.
The inductance turned on truly for shuts off the signal the arrival to win the time, but incurred has come the next difficult problem, how namely limited the inductance flows the magnetic energy which in the process accumulated to release, the peak blanker was the volume very small component, although had 泻放 the magnetic energy function, but could not all depend upon it. This article proposes two choices methods:
Method 1:
In inductance parallel fast bidirectional crystal thyratron.
Method 2:
After 8 IGBT simultaneously closes 4 mu s in, lets four pipes take turns to lead passes, in order to 泻放 on the inductance L energy, the method 1 principle is simple, does not need to relate in detail. This article 2 has obtained satisfaction result with the method, presently summarizes as follows:
In four refer to K2, K3, K6, K7, outside four refer to K1, K4, K5, the K8 tube. After eight simultaneously close 4 mu s, outside four continue to close, in four, K2, K7 lead passes, like chart 4. Shows.

Inductance L 泻放 the return route is place - D2 - K2 - L - K7 - D7 -. After 2 mu s, K2, K7 shut off, K3, K6 lead passes, like chart 5 shows.
Inductance L 泻放 the return route is place - D6 - K6 - L - K3 - D3 -. After 2 mu s, two electric discharges return routes carry on the exchange, passes through several times of relapse, on the L energy may 泻放 with nothing left. Entire short-circuits the protection process probably to complete in 40~50 mu s.
Test result
The entire machine movement is good, the accent presses the scope, the frequency modulation scope all satisfies the user request. Under the rated voltage, suddenly short-circuits the load, the equipment is safe and sound. After several minutes, heavy newly opened machine, all is normal. Must want further to enhance short-circuits the protection speed not to be certainly difficult, so long as for changes into 51 monolithic integrated circuits the high speed monolithic integrated circuit then.
This kind did not fear short-circuits in the intermediate frequency pressed the power source already to have more than 10 in the oil field use, underwent the test which the adverse circumstance and short-circuited.